Bus voltage control method and system of optical storage DC micro-grid

Abstract

The invention relates to the technical field of micro-grid voltage control, in particular to a bus voltage control method and system of an optical storage direct current micro-grid. The method comprises the following steps: acquiring a direct-current bus voltage and a converter inductive current in an operation process; obtaining a current prediction deviation according to the bus voltage change rate and the inductive current at each moment; constructing a capacitance response basis matrix based on the variation of the bus voltage in the current time period and the bus voltage, determining a first energy value, judging whether an internal component caused by a capacitance parameter error and an external component caused by load disturbance are mixed or not, and if so, determining the current time period according to the current prediction deviation and the capacitance response basis matrix. Obtaining a capacitance value deviation current vector and a load disturbance current vector, and determining a component energy ratio; generating a control instruction based on the load disturbance current vector and the component energy ratio; and if not, generating a control instruction according to the current prediction deviation. According to the invention, the dynamic response speed and control precision of the bus voltage are improved.

Description

Technical Field

[0001] This invention relates to the field of microgrid voltage control technology, specifically to a method and system for controlling the bus voltage of a photovoltaic-storage DC microgrid. Background Technology

[0002] As an energy exchange hub connecting distributed renewable energy sources (such as photovoltaics) and critical loads (such as data centers and electric vehicle charging stations), the stability of the DC bus voltage of a photovoltaic-storage DC microgrid is a core indicator for measuring power quality.

[0003] In the actual operation of photovoltaic-storage DC microgrid systems, the microgrids face the following problems: constant power loads connected to the bus exhibit negative impedance characteristics. When the bus voltage drops due to disturbances, the load current increases instead. This positive feedback mechanism can easily cause a sharp drop in bus voltage or even system instability during sudden load changes. To suppress this fluctuation, a feedforward control strategy based on a current observer is often adopted, that is, adjusting the power output in advance by monitoring changes in load current in real time. In addition, traditional observers usually assume that the bus capacitor is a linear constant element. However, in modern microgrids that pursue high power density, the widely used large-capacity multilayer ceramic capacitors or some electrolytic capacitors have significant DC bias characteristics. That is, the effective capacitance value of the capacitor is not constant, but decreases nonlinearly with changes in the DC bus voltage applied across its terminals. In scenarios with wide voltage range operation or large voltage fluctuations, this nonlinear attenuation characteristic causes observers based on fixed parameter models to be unable to distinguish between the internal current deviation caused by changes in capacitance value and the external current deviation caused by sudden changes in the actual load. This results in the observer outputting false load disturbance signals, which introduces unnecessary control noise during steady-state operation and leads to incorrect compensation calculations during sudden load changes, causing overcompensated oscillations or undercompensated drops. Summary of the Invention

[0004] To address the issue of low control accuracy in existing methods for controlling the bus voltage of photovoltaic-storage DC microgrids, the present invention aims to provide a method and system for controlling the bus voltage of photovoltaic-storage DC microgrids. The specific technical solution adopted is as follows: In a first aspect, the present invention provides a method for controlling the bus voltage of a photovoltaic-storage DC microgrid, the method comprising the following steps: Obtain the DC bus voltage and converter inductor current during the operation of the photovoltaic-storage DC microgrid system; Based on the rate of change of bus voltage at each moment and the inductor current, the current prediction deviation at each moment is obtained; based on the change of bus voltage and bus voltage at all moments in the current time period, the capacitor response basis matrix is ​​constructed, and the first energy value of the current time period is determined. Based on the value of the first energy value, it is determined whether the current prediction deviation contains internal components caused by capacitor parameter errors and external components caused by load disturbances. If so, the capacitance deviation current vector and the load disturbance current vector are obtained according to the current prediction deviation and the capacitor response basis matrix. The component energy ratio is determined by combining the capacitance deviation current vector and the load disturbance current vector. Feedforward control commands are generated based on the load disturbance current vector and the component energy ratio. If there is no mixture, then a feedforward control command is generated based on the current prediction deviation.

[0005] Preferably, obtaining the current prediction deviation at each moment based on the bus voltage change rate and the inductor current includes: For any given moment, based on the reference capacitor parameters of the previous moment and the bus voltage change rate at any given moment, a predicted value for the capacitor current is obtained; the difference between the inductor current collected at any given moment and the predicted value for the capacitor current is taken as the current prediction deviation at any given moment.

[0006] Preferably, the step of constructing the capacitive response basis matrix based on the changes in bus voltage and bus voltage at all times within the current time period includes: Arrange the changes in bus voltage at all times within the current time period in chronological order to obtain the linear response basis vector; Calculate the first product of the bus voltage value and the corresponding bus voltage change at each moment in the current time period, and arrange the first products of all moments in the current time period in chronological order to obtain the nonlinear coupling basis vector; The linear response basis vector and the nonlinear coupling basis vector constitute the capacitance response basis matrix.

[0007] Preferably, determining the first energy value for the current time period includes: taking the sum of the squares of all elements of the linear response basis vector as the first energy value for the current time period.

[0008] Preferably, the step of determining whether the current prediction deviation contains internal components caused by capacitor parameter errors and external components caused by load disturbances based on the magnitude of the first energy value includes: If the first energy value is less than the preset noise floor threshold, it is determined that the current prediction deviation does not contain internal components caused by capacitor parameter errors or external components caused by load disturbances. If the first energy value is greater than or equal to the preset noise floor threshold, it is determined that the current prediction deviation contains an internal component caused by capacitor parameter error and an external component caused by load disturbance.

[0009] Preferably, obtaining the capacitance deviation current vector and the load disturbance current vector based on the current prediction deviation and the capacitor response basis matrix includes: Arrange the current prediction deviations at all times within the current time period in chronological order to form a current prediction deviation vector; Calculate the orthogonal projection operator that projects the current prediction deviation vector onto the subspace spanned by the capacitor response basis matrix; Multiplying the orthogonal projection operator with the current prediction deviation vector yields the capacitance deviation current vector characterizing the capacitor parameter error. The difference between the current prediction deviation vector and the capacitance deviation current vector is determined as the load disturbance current vector characterizing the external load disturbance.

[0010] Preferably, determining the component energy ratio by combining the capacitance deviation current vector and the load disturbance current vector includes: taking the square of the magnitude of the current prediction deviation vector as the total deviation energy; if the total deviation energy is less than a preset deviation threshold, then setting the component energy ratio to 0; if the total deviation energy is greater than or equal to the preset deviation threshold, then obtaining the component energy ratio based on the square of the magnitude of the load disturbance current vector and the square of the magnitude of the capacitance deviation current vector. The step of generating a feedforward control command based on the load disturbance current vector and the component energy ratio includes: extracting the load disturbance current component corresponding to the current moment from the load disturbance current vector; multiplying the component energy ratio by the load disturbance current component to obtain a feedforward compensation amount; and superimposing the feedforward compensation amount with the current command output by the voltage outer loop controller to generate a feedforward control command.

[0011] Preferably, generating feedforward control commands based on the current prediction deviation includes: The current prediction deviation at the current moment is used as the load disturbance current; The preset value is multiplied by the load disturbance current to obtain the feedforward compensation amount; the feedforward compensation amount is superimposed with the current command output by the voltage outer loop controller to generate the feedforward control command.

[0012] Preferably, after generating the feedforward control command, the method further includes: Determine whether the parameter update conditions are met at the current moment. If they are met, update the reference capacitor parameters based on the current capacitance deviation current component, bus voltage change, and preset normalization step size at the current moment. If they are not met, keep the reference capacitor parameters unchanged. The parameter update conditions are as follows: the absolute value of the bus voltage change rate at the current moment is greater than the preset update threshold, and the proportion of the component energy is less than the preset purity threshold.

[0013] In a second aspect, the present invention provides a bus voltage control system for a photovoltaic-storage DC microgrid, the system being used to implement the method described in the first aspect above, the system comprising: The data acquisition module is used to acquire the DC bus voltage and converter inductor current during the operation of the photovoltaic-storage DC microgrid system. The processing module is used to obtain the current prediction deviation at each moment based on the bus voltage change rate and the inductor current at each moment; construct the capacitor response basis matrix based on the bus voltage change and bus voltage at all moments in the current time period, and determine the first energy value of the current time period. The first control module is used to determine whether the current prediction deviation contains an internal component caused by capacitor parameter error and an external component caused by load disturbance based on the value of the first energy value. If they are mixed, the module obtains the capacitance deviation current vector and the load disturbance current vector based on the current prediction deviation and the capacitor response basis matrix; determines the component energy ratio by combining the capacitance deviation current vector and the load disturbance current vector; and generates a feedforward control command based on the load disturbance current vector and the component energy ratio. The second control module is used to generate feedforward control commands based on the current prediction deviation if there is no mixing.

[0014] The present invention has at least the following beneficial effects: This invention collects DC bus voltage and converter inductor current during the operation of a photovoltaic-storage DC microgrid, and calculates current prediction deviation based on the bus voltage change rate and inductor current at each moment. This allows for real-time reflection of the deviation information between the actual operating state of the system and the theoretical model. By constructing a capacitor response basis matrix based on the bus voltage change and the bus voltage, and calculating the first energy value, the invention achieves intelligent identification and classification of the causes of current prediction deviation, thereby accurately determining whether the deviation simultaneously includes internal components caused by capacitor parameter errors and external components caused by load disturbances. If both types of components are determined to exist simultaneously, the current prediction deviation and the capacitor response basis matrix are used to accurately separate them, obtaining the capacitance deviation current vector and the load disturbance current vector. The component energy ratio is further calculated, and finally, a feedforward control command with accurate compensation capability is generated based on the load disturbance current vector and the component energy ratio. This avoids the observation inaccuracy problem caused by the time-varying and nonlinear characteristics of capacitor parameters, improves the dynamic response speed and control accuracy of the bus voltage, and enhances the stability and robustness of the system under load changes and wide voltage range operating conditions. Attached Figure Description

[0015] To more clearly illustrate the technical solutions and advantages in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 A flowchart illustrating a method for controlling the bus voltage of a photovoltaic-storage DC microgrid, provided as an embodiment of the present invention; Figure 2 This is a structural block diagram of a bus voltage control system for a photovoltaic-storage DC microgrid provided in an embodiment of the present invention. Detailed Implementation

[0017] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the following detailed description of a bus voltage control method and system for a photovoltaic-storage DC microgrid based on the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0018] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0019] The following description, in conjunction with the accompanying drawings, details the specific scheme of the bus voltage control method and system for a photovoltaic-storage DC microgrid provided by this invention.

[0020] Example of a bus voltage control method for photovoltaic-storage DC microgrids: This embodiment proposes a bus voltage control method for a photovoltaic-storage DC microgrid, such as... Figure 1 As shown, the bus voltage control method of the photovoltaic-storage DC microgrid in this embodiment includes the following steps: Step S1: Obtain the DC bus voltage and converter inductor current during the operation of the photovoltaic-storage DC microgrid system.

[0021] During the operation of the photovoltaic-storage DC microgrid system, based on a digital control system (such as a DSP or FPGA platform), and using discrete time k as the unique timing index, the power switching action of the bidirectional DC / DC converter causes high-frequency ripple in the bus voltage and inductor current. Misalignment at sampling times leads to spurious phase deviations between voltage and current data, affecting the accuracy of subsequent decoupling algorithms. To ensure the temporal consistency of the observed data, the controller is configured in PWM carrier synchronous trigger mode. Specifically, the analog-to-digital converter inside the controller synchronously acquires the analog signals from the DC bus voltage sensor and inductor current sensor at each moment during the operation of the photovoltaic-storage DC microgrid system and converts them into digital quantities, thus obtaining the DC bus voltage and converter inductor current at each moment during the operation of the photovoltaic-storage DC microgrid system. In this embodiment, the system control frequency is 20kHz; in specific applications, the implementer can set this frequency according to specific circumstances.

[0022] Step S2: Based on the rate of change of bus voltage at each moment and the inductor current, obtain the current prediction deviation at each moment; based on the change in bus voltage and bus voltage at all moments in the current time period, construct the capacitor response basis matrix and determine the first energy value of the current time period.

[0023] After the photovoltaic-storage DC microgrid system is started, the preset nominal value of the capacitor hardware, such as 2200μF, is read from the controller's non-volatile memory (Flash or EEPROM) and assigned to the reference capacitor parameter of the previous moment at the first moment.

[0024] Considering that the actual bus capacitance value dynamically changes with operating conditions (such as bias voltage and temperature) during operation, while the traditional conservation equations rely on fixed parameters, a deviation occurs between the model-based current prediction and the sensor-measured value. This deviation physically combines the model error current caused by parameter misalignment with the disturbance current caused by sudden changes in external load. The following section quantifies this deviation.

[0025] The following explanation uses a specific moment as an example; the method provided in this embodiment can be used to process other moments as well.

[0026] For the k-th time, the predicted value of the capacitor current is obtained based on the reference capacitor parameters of the previous time and the bus voltage change rate at this time; the difference between the inductor current collected at this time and the predicted value of the capacitor current is taken as the current prediction deviation at this time.

[0027] In this embodiment, a specific formula for calculating the current prediction error is given. The specific formula for calculating the current prediction error at time k can be expressed as: in, This represents the current prediction error at time k. This represents the inductor current sampled at time k. This represents the reference capacitance parameter at time k-1. This represents the bus voltage at time k. This represents the bus voltage at time k-1. This indicates the duration of each moment.

[0028] This represents the change in bus voltage at time k. This represents the rate of change of the bus voltage at time k. This represents the predicted capacitor current. It should be noted that for the first moment of operation of the photovoltaic-storage DC microgrid system, the change in bus voltage at that moment is set to zero.

[0029] If the k-th time is in a steady state and the predicted capacitor current is closer to the measured current, the current prediction deviation will be closer to zero; if a sudden load change or parameter drift occurs, the current prediction deviation will show a significant non-zero value.

[0030] To accurately identify patterns based on the system's dynamic characteristics and ultimately achieve accurate control, data within a time period is acquired. Considering that a time period that is too short is susceptible to random noise interference, while a time period that is too long results in excessive computation and a smoothing effect on the dynamic response, this embodiment uses 20 consecutive sampling moments as the duration of a single time period. The current time period is the 20 consecutive sampling moments ending at the current moment. It should be noted that in this embodiment, the number of sampling moments between the current moment and the start-up moment of the DC-DC storage system is greater than or equal to 20. If the number of sampling moments between the current moment and the start-up moment of the DC-DC storage system is less than 20, steps S2 and S3 are skipped, and the system is directly determined to be free of internal components caused by capacitor parameter errors and external components caused by load disturbances. In specific applications, the implementer can set the time period length according to the specific circumstances.

[0031] The effective capacitance of large-capacity ceramic or electrolytic capacitors changes significantly with the terminal voltage, exhibiting DC-Bias characteristics. To accurately describe this physical phenomenon, a first-order Taylor expansion is introduced to model the capacitor characteristics.

[0032] Assuming the capacitor operates near its current operating voltage, its capacitance function can be approximated as: ,in, This represents the instantaneous equivalent capacitance when the DC bus voltage is v. Based on the linear capacitance (constant term). Indicates voltage. This is a first-order nonlinear coefficient used to characterize the slope of capacitance change with voltage. Based on the definition of capacitor current, and neglecting higher-order terms in an engineering approximation, the actual capacitor current can be derived as: in, The capacitor current is represented by t, and time is represented by t. This represents the first derivative of the bus voltage v with respect to time t.

[0033] As can be seen from the above formula, the capacitor current consists of two parts: the linear response component and the linear response component. Nonlinear coupling components Among them, the linear response component is directly proportional to the voltage change rate, while the nonlinear coupling component is inversely proportional to the product of the voltage amplitude and the voltage change rate.

[0034] Based on the above characteristics, the changes in bus voltage at all times within the current time period are arranged in chronological order to obtain the linear response basis vector, which is used to characterize the linear charge and discharge characteristics. The linear response basis vector is a row vector, and the number of elements in the linear response basis vector is equal to the number of sampling times within the current time period.

[0035] Calculate the product of the bus voltage value at each moment within the current time period and the corresponding change in bus voltage at the same moment, denoted as the first product for each moment. The change in bus voltage at each moment within the current time period is the difference between the bus voltage at each moment and the bus voltage at the previous moment. Arrange all the first products within the current time period in chronological order to obtain the nonlinear coupling basis vector, which characterizes the nonlinear parameter coupling characteristics. The nonlinear coupling basis vector is a row vector, and the number of elements in the nonlinear coupling basis vector is equal to the number of sampling moments within the current time period.

[0036] The linear response basis vectors and the nonlinear coupling basis vectors constitute the capacitance response basis matrix, which can be expressed as: ,in, Represents the basis matrix of the capacitance response. Represents the basis vector of the linear response. Represents the nonlinearly coupled basis vector. The transpose of the vector is represented by the basis matrix of the capacitance response, which is a K-row, two-column matrix where K is the number of sampling times in the current time period.

[0037] The vectors in the two columns of the capacitor response basis matrix span a two-dimensional subspace. This subspace encompasses the main current response characteristics of the capacitor over a wide voltage range and under nonlinear conditions. Theoretically, any current change conforming to the physical laws of capacitance should lie within this subspace. The sum of the squares of all elements of the linear response basis vector is taken as the first energy value for the current time period. Since the linear response component dominates the total energy, the nonlinear term is merely a perturbation. Therefore, calculating only the energy of the linear component is sufficient to quickly and accurately characterize the voltage dynamic activity (noise floor level) of the system, and can significantly reduce computational resource consumption.

[0038] Step S3: Based on the value of the first energy value, determine whether the current prediction deviation contains an internal component caused by capacitor parameter error and an external component caused by load disturbance. If so, obtain the capacitance deviation current vector and the load disturbance current vector based on the current prediction deviation and the capacitor response basis matrix; determine the component energy ratio by combining the capacitance deviation current vector and the load disturbance current vector; and generate a feedforward control command based on the load disturbance current vector and the component energy ratio.

[0039] To ensure numerical stability in the system steady state (voltage remains basically unchanged) or in the early stages of data accumulation, and to ensure zero-delay response to sudden loads, the following will be done by comparing the first energy value with the preset noise floor threshold to determine whether the current prediction deviation contains internal components caused by capacitor parameter errors and external components caused by load disturbances.

[0040] Specifically, if the first energy value obtained in step S2 is less than the preset noise floor threshold, it indicates that the bus voltage is in a stable state, and the theoretical value of the capacitor current should be close to zero. If a significant current deviation is observed at this time, the deviation originates from a sudden change in the external load. Therefore, it is determined that the current prediction deviation does not contain internal components caused by capacitor parameter errors or external components caused by load disturbances. If the first energy value is greater than or equal to the preset noise floor threshold, it indicates that the bus voltage is undergoing a significant change, and the capacitor current component cannot be ignored. The current deviation is a mixture of parameter errors and load disturbances. Therefore, it is determined that the current prediction deviation contains internal components caused by capacitor parameter errors and external components caused by load disturbances. The preset noise floor threshold is usually taken as 3 to 5 times the quantization noise variance of the system voltage sampling channel. In this embodiment, the preset noise floor threshold is 0.001. In specific applications, the implementer can set it according to the specific situation.

[0041] When the current prediction error contains both an internal component caused by capacitor parameter errors and an external component caused by load disturbances, the mixed error can be decomposed into these two orthogonal components using the principle of geometric projection. To extract the component that conforms to the physical characteristics of the capacitor from the mixed error, it is necessary to calculate the projection matrix onto the capacitor response subspace.

[0042] Specifically, the current prediction deviations at all times within the current time period are arranged in chronological order to form a current prediction deviation vector. This vector is a K-row, 1-column vector. The elements in the first row of the vector represent the current prediction deviation at the first time point within the current time period, the elements in the second row represent the current prediction deviation at the second time point, and so on. An orthogonal projection operator is then calculated to project the current prediction deviation vector onto the subspace spanned by the capacitive response basis matrix.

[0043] In practical calculations, to prevent the matrix from approaching singularity due to the approximate collinearity of basis vectors, such as when the voltage changes linearly, the linear basis and the nonlinear basis may have a high correlation. Therefore, Tikhonov regularization is introduced for the calculation.

[0044] As a concrete example, the specific calculation formula for the orthogonal projection operator is given. The orthogonal projection operator can be expressed as: in, This represents the orthogonal projection operator. Let T denote the basis matrix of the capacitance response, and let T denote the transpose of the matrix. Represents the regularization coefficient. The identity matrix is ​​a single matrix. The identity matrix.

[0045] The range of values ​​for the regularization coefficient is: In this embodiment, the regularization coefficient is set to a value of 1. In practical applications, implementers can configure the settings according to specific circumstances. This embodiment ensures that matrix inversion is stable and bounded even under weak excitation conditions through regularization processing.

[0046] After obtaining the orthogonal projection operator through the above method, the current prediction deviation vector is then decomposed using the orthogonal projection operator.

[0047] Specifically, multiplying the orthogonal projection operator by the current prediction deviation vector yields the capacitance deviation current vector, which characterizes the capacitor parameter error. This vector represents the projection of the current prediction deviation vector onto the capacitor response subspace, physically corresponding to the current deviation caused by model parameter misalignment. Subtracting the capacitance deviation current vector from the current prediction deviation vector yields the load disturbance current vector, which characterizes external load disturbances. This load disturbance current vector represents the residual directly in the capacitor response subspace, physically corresponding to external load abrupt changes independent of voltage dynamics.

[0048] Using the above method, the accurate separation of intrinsic components that are strongly correlated with voltage dynamics and extrinsic components that are not correlated with voltage dynamics can be achieved.

[0049] To prevent calculation divergence when the system is unloaded or has only a weak noise floor, the energy proportion of the load component in the total deviation will be determined next, that is, the component energy proportion, to provide a quantitative reliability index for the subsequent control stage.

[0050] Specifically, the square of the magnitude of the current prediction deviation vector is calculated, and this square is taken as the total deviation energy. If the total deviation energy is less than a preset deviation threshold, it indicates that there is no significant current deviation, and all small fluctuations are noise. In this case, the component energy ratio is set to 0. The preset deviation threshold can be taken as the sum of squares of the quantization noise of the current sensor, which is generally 1%-2% of the system rated current. In this embodiment, the preset deviation threshold is [value missing]. In specific applications, implementers can set the parameters according to the specific circumstances. If the total deviation energy is greater than or equal to the preset deviation threshold, it indicates that there is an effective current deviation. At this time, the square of the magnitude of the load disturbance current vector and the square of the magnitude of the capacitance deviation current vector are calculated respectively. Based on the square of the magnitude of the load disturbance current vector and the square of the magnitude of the capacitance deviation current vector, the component energy ratio is obtained.

[0051] As a concrete example, the specific formula for calculating the component energy percentage is given. The component energy percentage can be expressed as: in, Indicates the percentage of energy contained in a component. This represents the load disturbance current vector. This represents the capacitance deviation current vector. This represents the magnitude of the load disturbance current vector. This represents the magnitude of the capacitance deviation current vector. This indicates a parameter for preventing zeroing.

[0052] In this embodiment, the value of the zero-prevention parameter is... In practical applications, implementers can set the parameters according to specific circumstances. The larger the value of the component energy percentage, the more likely the current deviation is to originate from sudden changes in the external load; the smaller the value of the component energy percentage, the more likely the current deviation is to originate from model parameter errors.

[0053] When the current deviation originates from a sudden change in load, full compensation is applied; if the deviation is mainly due to parameter errors or noise, the compensation amount is automatically reduced to prevent overcompensation oscillations caused by model errors.

[0054] The load disturbance current component corresponding to the current moment is extracted from the load disturbance current vector. This component is the last element in the load disturbance current vector. The product of the component's energy percentage and the current-moment load disturbance current component is used as the feedforward compensation. The current value output by the outer voltage loop controller is obtained, and the sum of the feedforward compensation and the current value output by the outer voltage loop controller is used as the target current value. This target current value is directly fed into the inner current loop controller to drive the bidirectional DC / DC converter to adjust its duty cycle. Since the feedforward compensation eliminates parameter error components, this feedforward action can accurately match sudden changes in load power, providing necessary current support before a significant drop in bus voltage occurs.

[0055] Step S4: If there is no mixture, then generate a feedforward control command based on the current prediction deviation.

[0056] When the current prediction deviation does not contain internal components caused by capacitor parameter errors and external components caused by load disturbances, the current prediction deviation at the current moment is taken as the load disturbance current. The preset value is multiplied by the load disturbance current to obtain the feedforward compensation amount. In this embodiment, the preset amount is 1, which is equivalent to setting the component energy ratio to 1. The sum of the feedforward compensation amount and the current value output by the voltage outer loop controller at the current moment is used as the target current value. The target current value is directly sent to the current inner loop controller to drive the bidirectional DC / DC converter to adjust the duty cycle.

[0057] To eliminate model mismatch caused by capacitor aging, temperature changes, or DC bias, the reference capacitor parameters are corrected using the separated capacitance deviation current. To ensure the accuracy of parameter updates, this embodiment introduces strict excitation constraints.

[0058] Given that the absolute value of the bus voltage change is too small to ensure that the system has sufficient voltage dynamics to identify capacitor parameters; the energy component is small enough to indicate that the current deviation is mainly dominated by parameter error rather than by severe load disturbance.

[0059] Based on the above characteristics, parameter update conditions are set as follows: the absolute value of the current bus voltage change rate is greater than a preset update threshold, and the component energy ratio is less than a preset purity threshold. It is determined whether the parameter update conditions are met at the current moment. If the conditions are met, the reference capacitor parameters are updated based on the current capacitance deviation current component, the bus voltage change, and the preset normalization step size. If the conditions are not met, it indicates that the system is in steady state or experiencing a drastic load change; in this case, the reference capacitor parameters are kept unchanged. In this embodiment, the preset update threshold is set to 800V / s, and the preset purity threshold is 0.5. In specific applications, the implementer can set these values ​​according to the specific circumstances.

[0060] When the parameter update conditions are met, the reference capacitor parameters can be updated according to the physical characteristics of the capacitor in the following ways: in, This indicates the updated reference capacitance parameters. This represents the reference capacitance parameter from the previous time step. This indicates the preset normalization step size. This represents the change in bus voltage at the current moment. This represents the current component representing the capacitance deviation at the current moment. This represents the bus voltage at the current moment. This represents the bus voltage at the previous time step. Represents a symbolic function.

[0061] In this embodiment, the preset normalization step size is 1. . Indicates the rate of change of voltage. It is used to characterize the direction of voltage change, and the error signal is demodulated using the direction of voltage change. The component that is strongly correlated with the dynamics of the capacitor is extracted and used to correct the model.

[0062] In order to maintain the continuous operation of the "observation-decoupling-control" closed loop, it is necessary to ensure that the observation model always follows the physical changes of the capacitor.

[0063] The system writes the new reference capacitance parameters (either the updated or retained reference capacitance parameters) into the controller's non-volatile status register, overwriting the old value. When the next digital control interrupt is triggered, the value in this register is read as the reference capacitance parameter for the next round of current prediction deviation calculation. Through this recursive feedback mechanism, as the system runs, the reference capacitance parameters gradually converge to the true physical value of the capacitance, thus ensuring the accuracy of the base construction and the effectiveness of decoupling. This closed-loop self-healing mechanism eliminates the need for manual recalibration throughout the control system's lifecycle, exhibiting strong robustness.

[0064] Thus, by using the method provided in this embodiment, the bus voltage of the photovoltaic-storage DC microgrid has been controlled.

[0065] This embodiment collects DC bus voltage and converter inductor current during the operation of the photovoltaic-storage DC microgrid, and calculates current prediction deviation based on the bus voltage change rate and inductor current at each moment. This can reflect the deviation information between the actual operating state of the system and the theoretical model in real time. By constructing a capacitor response basis matrix based on the bus voltage change and the bus voltage and calculating the first energy value, the causes of current prediction deviation are intelligently identified and classified, thereby accurately determining whether the deviation simultaneously includes internal components caused by capacitor parameter errors and external components caused by load disturbances. If both types of components are determined to exist simultaneously, the current prediction deviation and the capacitor response basis matrix are used to accurately separate them, obtaining the capacitance deviation current vector and the load disturbance current vector. The component energy ratio is further calculated, and finally, a feedforward control command with accurate compensation capability is generated based on the load disturbance current vector and the component energy ratio. This avoids the observation inaccuracy problem caused by the time-varying and nonlinear characteristics of capacitor parameters, improves the dynamic response speed and control accuracy of the bus voltage, and enhances the stability and robustness of the system under load changes and wide voltage range operating conditions.

[0066] Example of a bus voltage control system for a photovoltaic-storage DC microgrid: See Figure 2 The diagram illustrates a structural block diagram of a bus voltage control system for a photovoltaic-storage DC microgrid according to an embodiment of the present invention. The system may include a data acquisition module, a processing module, a first control module, and a second control module.

[0067] Among them, the data acquisition module is used to acquire the DC bus voltage and converter inductor current during the operation of the photovoltaic-storage DC microgrid system; The processing module is used to obtain the current prediction deviation at each moment based on the bus voltage change rate and the inductor current at each moment; construct the capacitor response basis matrix based on the bus voltage change and bus voltage at all moments in the current time period, and determine the first energy value of the current time period. The first control module is used to determine whether the current prediction deviation contains an internal component caused by capacitor parameter error and an external component caused by load disturbance based on the value of the first energy value. If they are mixed, the module obtains the capacitance deviation current vector and the load disturbance current vector based on the current prediction deviation and the capacitor response basis matrix; determines the component energy ratio by combining the capacitance deviation current vector and the load disturbance current vector; and generates a feedforward control command based on the load disturbance current vector and the component energy ratio. The second control module is used to generate feedforward control commands based on the current prediction deviation if there is no mixing.

[0068] It should be understood that Figure 2The structural block diagram and modules of the bus voltage control system of the photovoltaic-storage DC microgrid shown can be implemented in various ways. For example, in some embodiments, the system and its modules can be implemented by hardware, software, or a combination of software and hardware. The hardware portion can be implemented using dedicated logic; the software portion can be stored in memory and executed by appropriate instructions, such as a microprocessor or dedicated hardware. Those skilled in the art will understand that the above-described methods and apparatus can be implemented using computer-executable instructions and / or included in processor control code, for example, such code provided on a carrier medium such as a disk, CD, or DVD-ROM, a programmable memory such as read-only memory (firmware), or a data carrier such as an optical or electronic signal carrier. The apparatus and modules of this specification can be implemented not only by hardware circuits such as very large-scale integrated circuits or gate arrays, semiconductors such as logic chips, transistors, or programmable hardware devices such as field-programmable gate arrays, programmable logic devices, etc., but also by software executed by various types of processors, or by a combination of the above-described hardware circuits and software (e.g., firmware).

[0069] For more details about the above modules, please refer to other parts of this manual; they will not be repeated here.

[0070] It should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for controlling the bus voltage of a photovoltaic-storage DC microgrid, characterized in that, The method includes the following steps: Obtain the DC bus voltage and converter inductor current during the operation of the photovoltaic-storage DC microgrid system; Based on the rate of change of bus voltage at each moment and the inductor current, the current prediction deviation at each moment is obtained; based on the change in bus voltage and bus voltage at all moments in the current time period, the capacitor response basis matrix is ​​constructed, and the first energy value of the current time period is determined. Based on the value of the first energy value, it is determined whether the current prediction deviation contains internal components caused by capacitor parameter errors and external components caused by load disturbances. If so, the capacitance deviation current vector and the load disturbance current vector are obtained according to the current prediction deviation and the capacitor response basis matrix. The component energy ratio is determined by combining the capacitance deviation current vector and the load disturbance current vector. Feedforward control commands are generated based on the load disturbance current vector and the component energy ratio. If there is no mixture, then a feedforward control command is generated based on the current prediction deviation.

2. The bus voltage control method for a photovoltaic-storage DC microgrid according to claim 1, characterized in that, The step of obtaining the current prediction deviation at each moment based on the bus voltage change rate and the inductor current includes: For any given moment, based on the reference capacitor parameters of the previous moment and the bus voltage change rate at any given moment, a predicted value for the capacitor current is obtained; the difference between the inductor current collected at any given moment and the predicted value for the capacitor current is taken as the current prediction deviation at any given moment.

3. The bus voltage control method for a photovoltaic-storage DC microgrid according to claim 1, characterized in that, The construction of the capacitor response basis matrix based on the changes in bus voltage and bus voltage at all times within the current time period includes: Arrange the changes in bus voltage at all times within the current time period in chronological order to obtain the linear response basis vector; Calculate the first product of the bus voltage value and the corresponding bus voltage change at each moment in the current time period, and arrange the first products of all moments in the current time period in chronological order to obtain the nonlinear coupling basis vector; The linear response basis vector and the nonlinear coupling basis vector constitute the capacitance response basis matrix.

4. The bus voltage control method for a photovoltaic-storage DC microgrid according to claim 3, characterized in that, Determining the first energy value for the current time period includes: taking the sum of the squares of all elements of the linear response basis vector as the first energy value for the current time period.

5. The bus voltage control method for a photovoltaic-storage DC microgrid according to claim 1, characterized in that, The step of determining whether the current prediction deviation contains internal components caused by capacitor parameter errors and external components caused by load disturbances based on the magnitude of the first energy value includes: If the first energy value is less than the preset noise floor threshold, it is determined that the current prediction deviation does not contain internal components caused by capacitor parameter errors or external components caused by load disturbances. If the first energy value is greater than or equal to the preset noise floor threshold, it is determined that the current prediction deviation contains an internal component caused by capacitor parameter error and an external component caused by load disturbance.

6. The bus voltage control method for a photovoltaic-storage DC microgrid according to claim 1, characterized in that, The step of obtaining the capacitance deviation current vector and the load disturbance current vector based on the current prediction deviation and the capacitor response basis matrix includes: Arrange the current prediction deviations at all times within the current time period in chronological order to form a current prediction deviation vector; Calculate the orthogonal projection operator that projects the current prediction deviation vector onto the subspace spanned by the capacitor response basis matrix; Multiplying the orthogonal projection operator with the current prediction deviation vector yields the capacitance deviation current vector characterizing the capacitor parameter error. The difference between the current prediction deviation vector and the capacitance deviation current vector is determined as the load disturbance current vector characterizing the external load disturbance.

7. The bus voltage control method for a photovoltaic-storage DC microgrid according to claim 6, characterized in that, The step of determining the component energy ratio by combining the capacitance deviation current vector and the load disturbance current vector includes: taking the square of the magnitude of the current prediction deviation vector as the total deviation energy; if the total deviation energy is less than a preset deviation threshold, then setting the component energy ratio to 0; if the total deviation energy is greater than or equal to the preset deviation threshold, then obtaining the component energy ratio based on the square of the magnitude of the load disturbance current vector and the square of the magnitude of the capacitance deviation current vector. The step of generating a feedforward control command based on the load disturbance current vector and the component energy ratio includes: extracting the load disturbance current component corresponding to the current moment from the load disturbance current vector; multiplying the component energy ratio by the load disturbance current component to obtain a feedforward compensation amount; and superimposing the feedforward compensation amount with the current command output by the voltage outer loop controller to generate a feedforward control command.

8. The bus voltage control method for a photovoltaic-storage DC microgrid according to claim 1, characterized in that, The step of generating feedforward control commands based on the current prediction deviation includes: The current prediction deviation at the current moment is used as the load disturbance current; The preset value is multiplied by the load disturbance current to obtain the feedforward compensation amount; the feedforward compensation amount is superimposed with the current command output by the voltage outer loop controller to generate the feedforward control command.

9. The bus voltage control method for a photovoltaic-storage DC microgrid according to claim 1, characterized in that, After generating the feedforward control command, the following is also included: Determine whether the parameter update conditions are met at the current moment. If they are met, update the reference capacitor parameters based on the current capacitance deviation current component, bus voltage change, and preset normalization step size at the current moment. If they are not met, keep the reference capacitor parameters unchanged. The parameter update conditions are as follows: the absolute value of the bus voltage change rate at the current moment is greater than the preset update threshold, and the proportion of the component energy is less than the preset purity threshold.

10. A bus voltage control system for a photovoltaic-storage DC microgrid, the system being used to implement the method of claim 1, characterized in that, The system includes: The data acquisition module is used to acquire the DC bus voltage and converter inductor current during the operation of the photovoltaic-storage DC microgrid system. The processing module is used to obtain the current prediction deviation at each moment based on the bus voltage change rate and the inductor current at each moment; construct the capacitor response basis matrix based on the bus voltage change and bus voltage at all moments in the current time period, and determine the first energy value of the current time period. The first control module is used to determine whether the current prediction deviation contains an internal component caused by capacitor parameter error and an external component caused by load disturbance based on the value of the first energy value. If they are mixed, the module obtains the capacitance deviation current vector and the load disturbance current vector based on the current prediction deviation and the capacitor response basis matrix; determines the component energy ratio by combining the capacitance deviation current vector and the load disturbance current vector; and generates a feedforward control command based on the load disturbance current vector and the component energy ratio. The second control module is used to generate feedforward control commands based on the current prediction deviation if there is no mixing.

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