Direct current micro-grid stability control method considering constant power load

Abstract

The embodiment of the invention provides a DC micro-grid stability control method considering a constant power load, and relates to the technical field of power electronic equipment, and the method comprises the steps: building a state space model of a Boost DC-DC converter; constructing a linear active disturbance rejection controller; dC bus capacitor voltage is collected as a capacitor voltage measurement value; estimating the total disturbance of the system, and outputting a total disturbance observation value; the state feedback control unit executes duty ratio signal generation and output; discretization reconstruction is carried out on the linear active disturbance rejection controller, and a discretization control algorithm adaptive to the digital control chip is generated; capacitor voltage acquisition, disturbance observation value updating and duty ratio signal output are circularly completed according to a set sampling period. The technical problems that in the prior art, control parameters are generally designed and optimized based on a small signal model, large-range disturbance cannot be dealt with, the system is unstable under the large disturbance condition, and the reliability and safety of the micro-grid are seriously affected are solved.

Description

Technical Field

[0001] This invention relates to the field of power electronic equipment technology, and in particular to a method for stability control of a DC microgrid considering a constant power load. Background Technology

[0002] Microgrids, as a key component in the intelligent development of modern power systems, embody the technological direction of distributed energy integration and grid-coordinated power supply. With the widespread application of solar power generation devices, hydrogen fuel cells, energy storage equipment, and DC power terminals, DC microgrids are demonstrating their unique value in energy integration. Based on load characteristics, microgrid loads can be categorized into two main types: Constant Impedance (CIL) and Constant Power (CPL). Of particular note is that CPL typically manifests as power converters with closed-loop control, exhibiting a negative impedance effect at their input ports. This characteristic weakens the system's damping properties, potentially leading to instability in the distribution network and front-end converters, and even causing the entire system to collapse. Therefore, developing control schemes with rapid dynamic adjustment capabilities and the ability to maintain system stability is crucial to addressing this issue.

[0003] Traditional passive damping control strategies, while simple and reliable, suffer from drawbacks such as high cost and physical limitations. Active damping methods, on the other hand, achieve an equivalent damping effect by adjusting the control loop, but at the expense of the load's dynamic performance. Furthermore, most existing active damping schemes are based on small-signal models, guaranteeing stability only near the operating point and thus constituting local stability control. When the system encounters significant disturbances, these linear control methods may fail, leading to system instability. Therefore, researching novel control strategies for the stability of DC microgrids considering constant power loads has significant theoretical and engineering value.

[0004] It should be noted that the information disclosed in this background section is intended only to enhance the understanding of the overall background of the present invention, and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0005] To address the aforementioned deficiencies or improvement needs of existing technologies, this invention provides a stability control method for DC microgrids considering constant power loads. This method solves the technical problem that existing technologies typically design and optimize control parameters based on small-signal models. While theoretically ensuring system stability near the operating point, they are unable to cope with large-scale disturbances, leading to system instability or even collapse under significant disturbances, severely impacting the reliability and safety of the microgrid. The specific technical solution is as follows:

[0006] A stability control method for a DC microgrid considering constant power load is provided. The method includes: establishing a state-space model of a Boost DC-DC converter; constructing a linear active disturbance rejection controller (ADC controller) based on the state-space model, wherein the ADC controller includes a disturbance observer and a state feedback control unit, which are coupled in a closed loop through control signals and observation signals; acquiring the DC bus capacitor voltage as a measured value; inputting the measured value into the disturbance observer of the ADC controller to estimate the total system disturbance and outputting a total disturbance observation value; after receiving the total disturbance observation value, the state feedback control unit generates and outputs a duty cycle signal, wherein the duty cycle signal is input to the disturbance observer to participate in the total disturbance estimation and drive the Boost DC-DC converter; discretizing and reconstructing the ADC controller to generate a discretized control algorithm adapted to a digital control chip; and executing the discretized control algorithm through the digital control chip to cyclically complete capacitor voltage acquisition, disturbance observation value update, and duty cycle signal output according to a set sampling period.

[0007] In one implementation, after receiving the total disturbance observation, the state feedback control unit further performs the following processing:

[0008] S1: Calculate the real-time voltage error between the target voltage reference value and the measured capacitor voltage value; S2: Calculate the voltage error derivative based on the real-time voltage error; S3: Calculate the basic adjustment command based on the real-time voltage error and the voltage error derivative; S4: Dynamically calculate the control gain of the state-space model, and calculate the compensation command based on the total disturbance observation value and the control gain; S5: Generate the duty cycle signal by superimposing the compensation command and the basic adjustment command.

[0009] In one implementation, a state-space model of the Boost DC-DC converter is established, and the following processing is performed:

[0010] If the power supply system is in continuous conduction mode, the inductor current and capacitor voltage are used as state variables, and a spatial state model is established using the state-space averaging method; wherein, the state equation of the spatial state model is as follows:

[0011]

[0012] Among them, i L V is the inductor current. C V is the capacitor voltage. in P is the input voltage. CPL Here, represents the constant power load power, u is the duty cycle signal, L is the inductance value, and C is the capacitance value. This is a negative impedance disturbance term, used to characterize the instability effect of a power supply system caused by a constant power load.

[0013] In one implementation, the perturbation observer is a third-order linear extended state observer, and the continuous domain model of the third-order linear extended state observer is:

[0014]

[0015] Where z is the state observation vector, z = [z1z2z3] T z1 is the observed value of vC, z2 is the differential observed value of vC, z3 is the observed value of the total disturbance, and y = vC. For the observed value of vC;

[0016]

[0017] B = [0b00] T ;

[0018] C =

[100] ;

[0019] Where A, B, and C are the power supply system matrices, and b0 is the control gain.

[0020]

[0021] Where L is the observation gain, ω0 is the bandwidth of the third-order linear extended state observer, and ω0 = 5ω c ω c This is the cutoff frequency of the power supply system.

[0022] In one embodiment, the state feedback control unit consists of a controller and a compensation circuit, and is responsible for generating the duty cycle signal.

[0023] In one implementation, the following processing is also performed:

[0024] The controller employs proportional-derivative (PD) control; the controller's output formula is as follows:

[0025] u0 = k p (r-z1)-k d z2;

[0026] Where u0 is the basic adjustment command, r is the target voltage reference value, and k p k is the proportional gain of the controller. d Let be the differential gain of the controller, and satisfy . k d =2ξω c ξ is the damping ratio, ξ∈[0.7,1.0];

[0027] The closed-loop transfer function of the controller is as follows:

[0028]

[0029] Wherein, G(s) represents the target voltage reference value to v C The closed-loop transfer function of the observed values, where s is a complex frequency variable.

[0030] In one implementation, the following processing is also performed:

[0031] The total disturbance observation value output by the disturbance observer is input into the compensation circuit to calculate the compensation command. Where b0 is the control gain of the state-space model, and Δu is the disturbance compensation amount as the compensation command;

[0032] The duty cycle signal is generated by superimposing the compensation command and the basic adjustment command, as follows:

[0033]

[0034] Where u is the duty cycle signal.

[0035] In one implementation, the dynamic calculation formula for the control gain is as follows:

[0036]

[0037] in, This is the partial derivative of the second derivative of the capacitor voltage with respect to the empty percentage signal. It is determined by the parameters of the Boost type DC-DC converter.

[0038] Beneficial effects of the embodiments of the present invention:

[0039] In the solution provided by this invention, a state-space model of the Boost-type DC-DC converter is established to accurately describe the dynamic behavior of the converter. This model uses the state-space averaging method, enabling the system to better reflect voltage and current changes during actual operation. Based on the state-space model, a linear active disturbance rejection controller (ADC) is constructed, including a disturbance observer and a state feedback control unit. The disturbance observer is used to estimate the total disturbance of the system, and the state feedback control unit generates control signals based on the observed values. This closed-loop coupling effectively suppresses load disturbances, especially the negative impedance effect caused by constant power loads. Real-time acquisition of the DC bus capacitor voltage as a capacitor voltage measurement value allows direct monitoring of capacitor voltage changes, providing necessary measurement data for the disturbance observer and supporting disturbance estimation. The disturbance observer estimates the total system disturbance based on the capacitor voltage measurement value and outputs the total disturbance observation value. The disturbance observer can capture and analyze disturbances caused by constant power loads in the power grid, providing accurate disturbance estimation. The system calculates and ensures that subsequent control units can respond quickly based on this information, thereby maintaining system stability. Based on the total disturbance observation, the state feedback control unit generates a duty cycle signal and drives the Boost DC-DC converter. By precisely adjusting the duty cycle signal, the controller can achieve real-time voltage regulation, quickly respond to disturbances caused by load changes, and maintain the stable operation of the power grid. The linear active disturbance rejection controller is discretized and reconstructed to generate a discretized control algorithm adapted to the digital control chip. Through discretization, the controller's control strategy can be executed efficiently in the form of digital signals, achieving precise control in the microgrid system. The digital control chip executes the discretized control algorithm and cyclically completes capacitor voltage acquisition, disturbance observation update, and duty cycle signal output according to the set sampling period. The efficient execution of digital control ensures that the system responds to load changes in real time and makes adjustments within each sampling period, enabling the system to adapt to load changes and disturbances more quickly, ensuring the stable operation of the microgrid in dynamic environments.

[0040] Of course, implementing any product or method of the present invention does not necessarily require achieving all of the advantages described above at the same time. Attached Figure Description

[0041] To more clearly illustrate the technical solutions 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.

[0042] Figure 1 This invention provides a schematic flowchart of a DC microgrid stability control method considering constant power loads.

[0043] Figure 2 The diagram shows a flow chart of generating duty cycle signals in a DC microgrid stability control method considering constant power load provided by the present invention.

[0044] Figure 3 This diagram illustrates the operation results of a DC microgrid stability control method considering constant power load provided by the present invention under constant power load disturbance.

[0045] Figure 4 The diagram shows the operation results of a DC microgrid stability control method considering constant power load provided by the present invention under constant impedance load disturbance. Detailed Implementation

[0046] To facilitate understanding of the present invention, a more complete description of the invention will be given below with reference to the accompanying drawings, which illustrate preferred embodiments of the invention. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein; rather, these embodiments are provided so that the disclosure of the invention will be more thorough and complete.

[0047] Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0048] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0049] Unless otherwise expressly stated, throughout the specification and claims, the term "comprising" or its variations such as "including" or "comprises" shall be understood to include the stated elements or components without excluding other elements or other components.

[0050] This invention provides a DC microgrid stability control method considering constant power loads, which addresses the technical problem that existing technologies typically design and optimize control parameters based on small-signal models. While theoretically ensuring system stability near the operating point, these methods cannot cope with large-scale disturbances, leading to system instability or even collapse under significant disturbances, thus severely impacting the reliability and safety of the microgrid.

[0051] Example 1: See Figure 1 The present invention provides a flowchart of a DC microgrid stability control method considering a constant power load, the method comprising:

[0052] Y100: Establish the state-space model of the Boost DC-DC converter.

[0053] The simplified cascaded system architecture of a DC microgrid mainly consists of distributed generation units, a boost-type DC-DC converter, a constant impedance load (CIL), and a constant power load (CPL). The system operates in continuous conduction mode, and a state-space model is established based on the state-space averaging method.

[0054] Y200: A linear active disturbance rejection controller is constructed based on the state-space model, wherein the linear active disturbance rejection controller includes a disturbance observer and a state feedback control unit, and the disturbance observer and the state feedback control unit are coupled in a closed loop through control signals and observation signals.

[0055] Since constant power loads may introduce disturbances, such as negative impedance effects, it is necessary to estimate these disturbances in real time using a disturbance observer. These disturbances include changes both inside and outside the system, such as load fluctuations and input voltage disturbances, and these disturbances are not easily measured directly. A third-order linear extended state observer is used to estimate the total disturbance. The system disturbance is estimated by measuring the capacitor voltage, its derivative, and the observed total disturbance, thus providing information for subsequent control. The state feedback control unit is responsible for generating control signals based on the system's state information, including the capacitor voltage, and the disturbance observations. These signals include basic adjustment commands and compensation commands.

[0056] Y300: Collects the DC bus capacitor voltage as the capacitor voltage measurement value.

[0057] The DC bus capacitor voltage is acquired in real time using appropriate sensors or sampling circuits. This voltage value reflects the potential difference across the capacitor and is a crucial variable for the dynamic control of the Boost DC-DC converter. The acquired DC bus capacitor voltage serves as one of the inputs to the disturbance observer, participating in the estimation of the total disturbance and influencing the state feedback control unit. Through this feedback mechanism, the duty cycle can be adjusted in real time based on the actual voltage deviation, thereby maintaining the stability of the output voltage.

[0058] Y400: Input the measured capacitor voltage value into the disturbance observer of the linear active disturbance rejection controller to estimate the total system disturbance and output the total disturbance observation value.

[0059] The measured capacitor voltage value is input to the disturbance observer. Since the disturbance observer uses a third-order linear extended state observer, it estimates the disturbance using the capacitor voltage and its derivative (the differential of the voltage error). These disturbances are output through the model of the disturbance observer. Specifically, the disturbance observer uses the capacitor voltage and its derivative to calculate the total disturbance in the system and generates a total disturbance observation value. This total disturbance observation value reflects the impact of external disturbances on the system, such as load changes or input voltage changes. It serves as input to the subsequent control section, helping to adjust the duty cycle and counteract the system disturbance.

[0060] Y500: After receiving the total disturbance observation value, the state feedback control unit performs a duty cycle signal generation output, wherein the duty cycle signal is input to the disturbance observer to participate in the total disturbance estimation and drive the Boost DC-DC converter.

[0061] The state feedback control unit receives the total disturbance observation and calculates the control signal based on the error between the total disturbance observation and the capacitor voltage and target voltage reference values. The duty cycle signal is a key parameter for adjusting the output voltage of the Boost DC-DC converter, and it is generated by superimposing basic regulation commands and compensation commands. The generated duty cycle signal is used to control the switching of the Boost DC-DC converter, and the duty cycle controls the converter's output voltage to maintain consistency with the desired target voltage. The generated duty cycle signal not only drives the converter but is also fed back to the disturbance observer, participating in the total disturbance estimation loop. This feedback mechanism helps to continuously update the total disturbance observation to cope with changes and uncertainties in the system.

[0062] Y600: Discretize and reconstruct the linear active disturbance rejection controller to generate a discretized control algorithm adapted to the digital control chip.

[0063] In digital control systems, control algorithms are typically represented in discrete form for implementation on digital hardware. Continuous-time control algorithms cannot be directly applied to digital control chips, therefore discretization is necessary. The state-space model and controller design are transformed from the continuous-time domain to the discrete-time domain, which can be achieved through sampling periods. After discretization and reconstruction, the control algorithm adapts to the operating mode of the digital hardware, enabling real-time processing of sampled data and calculation of control signals. The discretized control algorithm generates a discrete control algorithm adapted to the digital control chip. The digital control chip executes these algorithms periodically, performing cyclical control according to a preset sampling period to ensure system stability.

[0064] Furthermore, the discretized observer can be represented as:

[0065] z(k)=A ESO ·z(k-1)+B ESO·u(k-1)+L ESO ·y(k);

[0066] in:

[0067]

[0068] Gain matrix L c The possible values ​​are as follows:

[0069]

[0070] The coefficient matrices A, B, and C can be discretized as follows:

[0071]

[0072] In the formula, T s This indicates the sampling period of the controller.

[0073] Y700: The discrete control algorithm is executed by the digital control chip to cyclically complete the acquisition of capacitor voltage, update of disturbance observation value and output of duty cycle signal according to the set sampling period.

[0074] In digital control systems, the control update frequency is determined by a set sampling period, typically ranging from a few microseconds to a few milliseconds, depending on the system's dynamic requirements and control objectives. Within each set sampling period, the digital control chip acquires the current value of the capacitor voltage and inputs it to the disturbance observer. The disturbance observer updates the total disturbance observation based on the new capacitor voltage and voltage derivative, which serves as the basis for generating the next control signal. The updated total disturbance observation is input to the state feedback control unit, which calculates the duty cycle signal based on the new disturbance observation and outputs it to the Boost DC-DC converter. This process is continuously executed cyclically according to the set sampling period, updating the capacitor voltage sampling, the disturbance observation, and the duty cycle signal in each cycle, ensuring stable system operation under dynamic loads and disturbances.

[0075] In one implementation, see Figure 2 After receiving the total disturbance observation, the state feedback control unit performs the following steps:

[0076] S1: Calculate the real-time voltage error between the target voltage reference value and the measured capacitor voltage value.

[0077] S2: Calculate the voltage error differential based on the real-time voltage error.

[0078] S3: Calculate the basic adjustment command based on the real-time voltage error and the voltage error derivative.

[0079] S4: Dynamically calculate the control gain of the state-space model, and calculate the compensation command based on the total disturbance observation and the control gain.

[0080] S5: By superimposing the compensation command and the basic adjustment command, a duty cycle signal is generated.

[0081] The target voltage reference value is the desired voltage preset during design, representing the expected DC bus voltage of the system. It is the target of the control system, and the controller's task is to adjust the output voltage as close to this target value as possible. The capacitor voltage measurement value is the current capacitor voltage acquired in real time by sensors. It reflects the output voltage of the Boost DC-DC converter, and the deviation from the target voltage reference value is the real-time voltage error. The real-time voltage error reflects the degree of deviation between the system's current output and the desired value, and this error will serve as the basis for subsequent control calculations.

[0082] The voltage error derivative is calculated based on the real-time voltage error, which is the rate of change of the voltage error over time. It is typically the derivative of the capacitor voltage, i.e., the instantaneous rate of change of the capacitor voltage. The voltage error derivative indicates the speed of the system response. If the capacitor voltage increases or decreases rapidly, the voltage error derivative will have a large value, indicating that the system is still far from the target voltage and requires stronger control. Conversely, a small voltage error derivative indicates that the system is stable and the change is gradual.

[0083] The basic regulation command is calculated using proportional gain and derivative gain via proportional-derivative (PD) control. Proportional control adjusts the voltage error to ensure the system approaches the desired target voltage as closely as possible. Derivative control suppresses rapid voltage changes, enhancing the system's dynamic response speed. The derivative term allows the controller to better predict voltage change trends, enabling earlier adjustments. This basic regulation command is the initial regulation command for the control system and does not yet consider disturbances and external factors.

[0084] In the state-space model, the control gain is a dynamic parameter related to system parameters (such as input voltage and load). This control gain is related to the rate of change of capacitor voltage and the influence of duty cycle. The dynamic calculation of the control gain is accomplished by solving the system state equations. The compensation command is calculated based on the total disturbance observations and the control gain. The generation of the compensation command is closely related to external disturbances, such as the negative impedance effect caused by a constant power load. The compensation command ensures that the system can still reach the expected voltage level when these disturbances are present.

[0085] The final control signal, the duty cycle signal, is obtained by superimposing the basic adjustment command and the compensation command. It is used to control the switching duty cycle of the Boost DC-DC converter. The duty cycle directly determines the ratio of the converter's output voltage to its input voltage, thereby adjusting the output voltage. By superimposing the basic adjustment command and the compensation command, the influence of external disturbances on the voltage can be effectively addressed, thus ensuring stable system operation and maintaining the capacitor voltage close to the desired value.

[0086] In one implementation, a state-space model of the Boost DC-DC converter is established, including:

[0087] Y110: If the power supply system is in continuous conduction mode, the inductor current and capacitor voltage are used as state variables, and a spatial state model is established using the state-space averaging method; wherein, the state equation of the spatial state model is as follows:

[0088]

[0089] Among them, i L V is the inductor current. C V is the capacitor voltage. in P is the input voltage. CPL Here, represents the constant power load power, u is the duty cycle signal, L is the inductance value, and C is the capacitance value. This is a negative impedance disturbance term, used to characterize the instability effect of a power supply system caused by a constant power load.

[0090] Inductor current is one of the main currents in a boost-type DC-DC converter, reflecting the converter's operating state and energy storage. As one of the system's state variables, inductor current directly affects the stability of voltage regulation. Capacitor voltage is the system's output voltage, directly affecting the voltage quality at the load end. Capacitor voltage is also one of the targets that the control system needs to track and regulate. These two variables determine the dynamic behavior of the boost-type DC-DC converter and are therefore chosen as state variables.

[0091] State-space averaging is a modeling method used in switching power supply control systems, particularly suitable for describing systems with periodic switching, such as DC-DC converters. By averaging the system states over the switching cycle, a simplified linear model can be obtained, facilitating analysis and control. In Boost DC-DC converters, the state-space model typically has two operating states: switch-on and switch-off. By weighted averaging the system state equations under these two states, the system's state-space model can be obtained.

[0092] The state equations of the space-state model describe the changes in inductor current and capacitor voltage over time, where the constant power load power PCPL This represents the demand of a constant power load on the system; negative impedance disturbance term. This is used to characterize the system instability effect caused by constant power load. This effect is due to the fact that constant power load has very strict requirements on the power supply voltage when the load voltage changes, which usually causes voltage oscillation or instability, especially when the system load changes.

[0093] Negative impedance disturbance term This is specifically introduced in the state-space model to describe the impact of a constant power load on a Boost DC-DC converter. Specifically, a constant power load requires a fixed power supply and significantly affects system stability when the voltage changes. This effect can be represented by negative impedance, i.e., the negative impedance effect. The constant power load power P... CPL Let be a known constant representing the load's power demand on the power supply, and be the negative impedance disturbance term. This negative impedance disturbance term can affect system stability, especially when the load fluctuates or changes, potentially causing voltage instability or overshoot. Therefore, introducing this term helps to account for the potential instability caused by constant power loads during modeling, enabling better compensation and stable control when designing the controller.

[0094] In one implementation, the perturbation observer is a third-order linear extended state observer, and the continuous domain model of the third-order linear extended state observer is:

[0095]

[0096] Where z is the state observation vector, z = [z1z2z3] T z1 is v C The observed value, z2 is v C The differential observation value, z3 is the total disturbance observation value, y = v C , For v C Observed values;

[0097]

[0098] B = [0b00] T ;

[0099] C =

[100] ;

[0100] Where A, B, and C are the power supply system matrices, and b0 is the control gain;

[0101]

[0102] Where L is the observation gain, ω0 is the bandwidth of the third-order linear extended state observer, and ω0 = 5ωc ω c This is the cutoff frequency of the power supply system.

[0103] The third-order linear extended state observer is an observation method that extends the traditional observer structure. It can estimate system disturbances and state variables by treating disturbances as virtual states of the system for estimation, thereby achieving effective compensation for disturbances and enhancing system stability. For complex systems like DC microgrids, which are often affected by external disturbances or load changes, the third-order linear extended state observer can effectively track these disturbances and take appropriate compensation measures. The state observation vector z of this disturbance observer consists of three parts: capacitor voltage v... C The observed values ​​z1, v C The differential observation value z2 and the total disturbance observation value z3.

[0104] In the continuous domain, the model of a third-order linear extended state observer can be represented as a linear system, where A, B, and C are the state-space matrices of the power supply system, used to describe the dynamic behavior of the system, and L is the observation gain, used to adjust the dynamic response and accuracy of the observer.

[0105] ω0 is the bandwidth of the third-order linear extended state observer, used to describe the observer's response to high-frequency disturbances. A larger bandwidth results in more accurate estimations of rapidly changing disturbances, but may also lead to oversensitivity of the system. Therefore, the bandwidth selection needs to balance response speed and system stability. ω0 = 5ω c ω c The cutoff frequency of the power supply system is used to describe the system's response to low-frequency disturbances. This cutoff frequency is closely related to the system's dynamic characteristics and control strategy, and usually needs to be selected according to the system's operating frequency.

[0106] In actual operation, the disturbance observer works as follows: First, it acquires the capacitor voltage v from the system. C That is, the system's output signal, which the observer receives through the system matrix A, B, C, control input u, and capacitor voltage v. C The system's states z1, z2, and disturbance z3 are estimated based on the feedback. Specifically, the disturbance term z3 can be considered as a disturbance estimate of the system, reflecting the impact of external disturbances. Disturbance compensation is performed using the observed total disturbance z to optimize the control signal and improve system stability. By adjusting the observation gain and bandwidth, the observer's performance can be flexibly controlled to adapt to different operating conditions.

[0107] In one implementation, the state feedback control unit consists of a controller and a compensation circuit, and is responsible for generating the duty cycle signal.

[0108] The state feedback control unit consists of a controller and a compensation circuit. Its main task is to generate the duty cycle signal for driving the Boost DC-DC converter. This control unit compares the real-time measured capacitor voltage with a set target voltage reference value and generates an adjustment signal based on the error, thereby adjusting the duty cycle. The controller uses proportional-derivative control, and the main function of the compensation circuit is to further optimize the system performance, especially when subjected to disturbances. It can adjust the duty cycle signal through compensation to stabilize the voltage output.

[0109] One implementation also includes:

[0110] Y521: The controller uses proportional-derivative control;

[0111] Y522: The output formula of the controller is as follows:

[0112] u0 = k p (r-z1)-k d z2;

[0113] Where u0 is the basic adjustment command, r is the target voltage reference value, and k p k is the proportional gain of the controller. d Let be the differential gain of the controller, and satisfy . k d =2ξω c ξ is the damping ratio, ξ∈[0.7,1.0];

[0114] Y523: The closed-loop transfer function of the controller is as follows:

[0115]

[0116] Wherein, G(s) represents the target voltage reference value to v C The closed-loop transfer function of the observed values, where s is a complex frequency variable.

[0117] The controller employs proportional-derivative control, and its control algorithm consists of two parts: a proportional term, which is proportional to the real-time voltage error and is responsible for the system's rapid response; and a derivative term, which is proportional to the derivative of the voltage error and provides the system's predictability, thereby improving system stability and reducing overshoot.

[0118] Based on the fundamental principle of proportional-derivative control, the output formula of the controller is as shown above. When designing the controller, the selection of the proportional term gain and the derivative term gain is crucial to the stability and response speed of the system. The proportional term gain is selected as the square of the system's cutoff frequency, and the derivative term gain is selected based on the damping ratio. The damping ratio ranges from [0.7, 1.0] and is used to adjust the transient response and stability of the system. A higher damping ratio provides a smoother response but may increase the response time, while a lower damping ratio may lead to a faster response but may result in overshoot.

[0119] The closed-loop transfer function of the controller describes the relationship between the target voltage reference value and the capacitor voltage. It reflects how the controller adjusts the output signal (capacitor voltage) according to the input signal (target voltage reference value) to achieve the desired effect.

[0120] One implementation also includes:

[0121] S51: Input the total disturbance observation value output by the disturbance observer into the compensation circuit to calculate the compensation command.

[0122] Where b0 is the control gain of the state-space model, and Δu is the disturbance compensation amount as the compensation command;

[0123] S52: The duty cycle signal is generated by superimposing the compensation command and the basic adjustment command, as follows:

[0124]

[0125] Where u is the duty cycle signal.

[0126] The disturbance observer has estimated the total disturbance in the system and outputs the total disturbance observation value z3, reflecting the impact of disturbances on the system, including load changes, input voltage fluctuations, and other factors. The total disturbance observation value z3 is input to the compensation stage, which uses z3 as input and the control gain b0 to calculate the disturbance compensation amount and generate a compensation command. The control gain b0 is part of the system parameters and is determined by the physical model of the Boost DC-DC converter. The negative sign here indicates that the compensation command is in the opposite direction to the total disturbance, aiming to use the compensation signal to cancel or reduce the impact of the disturbance on the system and restore system stability.

[0127] The final duty cycle signal is obtained by superimposing the basic adjustment command and the disturbance compensation command. This final duty cycle signal is used to drive the Boost DC-DC converter, thereby adjusting the output voltage to ensure that the system can respond quickly and remain stable. In this way, the compensation stage can dynamically adjust the duty cycle according to the real-time disturbance estimate, thereby effectively reducing the impact of disturbances on the system and ensuring system stability and precise control.

[0128] In one implementation, the dynamic calculation formula for the control gain is as follows:

[0129]

[0130] in, This is the partial derivative of the second derivative of the capacitor voltage with respect to the empty percentage signal. It is determined by the parameters of the Boost type DC-DC converter.

[0131] In a control system, the calculation of control gain determines the relationship between the duty cycle and the capacitor voltage, which directly affects the system's stability and dynamic response. This describes how the capacitor voltage changes with the duty cycle at a given input voltage. A larger control gain means that the effect of duty cycle changes on the capacitor voltage is more significant. The control gain is determined by the converter's inductance L and capacitance C, reflecting the converter's energy storage capacity. Specifically, inductance L affects the rate of current change; a larger inductance makes the current change smoother, thus affecting the duty cycle's response to the capacitor voltage. Capacitor C affects the smoothness of the voltage; a larger capacitance smooths voltage fluctuations better, thus affecting the change in capacitor voltage. Input voltage v in This affects the range of voltage variation; a higher input voltage leads to a larger capacitor voltage, which in turn affects the sensitivity of the duty cycle.

[0132] The calculation of control gain is dynamic, meaning that it changes with the state of the system. Under different operating conditions, the system needs different control gains to maintain stability and precise control, so as to ensure that the system can effectively cope with various disturbances and changes.

[0133] The stability control method for a DC microgrid considering a constant power load is verified as follows:

[0134] Operating Condition 1: Constant Power Load Disturbance Test.

[0135] The load disturbance was verified by measuring the step change of CPL under a mixed load (CPL+CIL). Initially, CIL and CPL were 40Ω and 600W, respectively. At 0.05s, CPL abruptly changed from 600W to 900W, recovered to 600W at 0.15s, dropped to 300W at 0.25s, and recovered to 600W at 0.35s. Figure 3 The results of the control method proposed in this invention under constant power load disturbance are shown. See also Figure 3 A CPL step disturbance will generate an instantaneous voltage deviation of approximately 3.2V. Under the control method, the voltage error is eliminated in about 10ms, and the DC bus voltage remains stable.

[0136] Operating Condition 2: Constant Impedance Load Disturbance Test.

[0137] To verify the system state of the DC microgrid under worst-case conditions, all CILs were removed to put the system in a negative damping state. The initial CPL of the system was 600W, and a CIL with a parameter of 40Ω was suddenly applied at 0.1s. All CILs were removed at 0.3s. Figure 4 The results of the control method proposed in this invention under constant impedance load disturbance are shown. See also Figure 4 The control method proposed in this invention generates only a 3.5V voltage deviation under CIL step disturbance, and the voltage deviation is eliminated in about 8ms. The bus voltage remains stable and has strong dynamic stability.

[0138] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

[0139] The foregoing description of specific exemplary embodiments of the invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A method for stability control of a DC microgrid considering a constant power load, characterized in that, include: Establish the state-space model of the Boost DC-DC converter; A linear active disturbance rejection controller is constructed based on the state-space model, wherein the linear active disturbance rejection controller includes a disturbance observer and a state feedback control unit, and the disturbance observer and the state feedback control unit are coupled in a closed loop through control signals and observation signals; The DC bus capacitor voltage is collected as the capacitor voltage measurement value; The measured capacitor voltage value is input into the disturbance observer of the linear active disturbance rejection controller to estimate the total system disturbance, and the total disturbance observation value is output. After receiving the total disturbance observation value, the state feedback control unit generates and outputs a duty cycle signal, wherein the duty cycle signal is input to the disturbance observer to participate in the total disturbance estimation and drives the Boost DC-DC converter. The linear active disturbance rejection controller is discretized and reconstructed to generate a discretized control algorithm adapted to the digital control chip; The discrete control algorithm is executed by the digital control chip to cyclically complete the acquisition of capacitor voltage, update of disturbance observation value and output of duty cycle signal according to the set sampling period.

2. The DC microgrid stability control method considering constant power load as described in claim 1, characterized in that, After receiving the total disturbance observation value, the state feedback control unit performs the following steps: S1: Calculate the real-time voltage error between the target voltage reference value and the measured capacitor voltage value; S2: Calculate the voltage error differential based on the real-time voltage error; S3: Calculate the basic adjustment command based on the real-time voltage error and the voltage error derivative; S4: Dynamically calculate the control gain of the state-space model, and calculate the compensation command based on the total disturbance observation and the control gain; S5: By superimposing the compensation command and the basic adjustment command, a duty cycle signal is generated.

3. The DC microgrid stability control method considering constant power load as described in claim 1, characterized in that, Establish the state-space model of the Boost DC-DC converter, including: If the power supply system is in continuous conduction mode, the inductor current and capacitor voltage are used as state variables, and the state space averaging method is used to establish a spatial state model. The state equation of the spatial state model is as follows: Among them, i L V is the inductor current. C V is the capacitor voltage. in P is the input voltage. CPL Here, represents the constant power load power, u is the duty cycle signal, L is the inductance value, and C is the capacitance value. This is a negative impedance disturbance term, used to characterize the instability effect of a power supply system caused by a constant power load.

4. The DC microgrid stability control method considering constant power load as described in claim 1, characterized in that, The disturbance observer is a third-order linear extended state observer, and the continuous domain model of the third-order linear extended state observer is as follows: Where z is the state observation vector, z = [z1z2z3] T z1 is v C The observed value, z2 is v C The differential observation value, z3 is the total disturbance observation value, y = v C , For v C Observed values; B=[0b00] T ; C＝[100]； Where A, B, and C are the power supply system matrices, and b0 is the control gain; Where L is the observation gain, ω0 is the bandwidth of the third-order linear extended state observer, and ω0 = 5ω c ω c This is the cutoff frequency of the power supply system.

5. The DC microgrid stability control method considering constant power load as described in claim 2, characterized in that, The state feedback control unit consists of a controller and a compensation circuit, and is responsible for generating the duty cycle signal.

6. The DC microgrid stability control method considering constant power load as described in claim 5, characterized in that, Also includes: The controller employs proportional-derivative control. The output formula of the controller is as follows: u0=k p (r-z1)-k d z2; Where u0 is the basic adjustment command, r is the target voltage reference value, and k p k is the proportional gain of the controller. d Let be the differential gain of the controller, and satisfy . k d =2ξω c ξ is the damping ratio, ξ∈[0.7,1.0]; The closed-loop transfer function of the controller is as follows: Wherein, G(s) represents the target voltage reference value to v C The closed-loop transfer function of the observed values, where s is a complex frequency variable.

7. The DC microgrid stability control method considering constant power load as described in claim 5, characterized in that, Also includes: The total disturbance observation value output by the disturbance observer is input into the compensation circuit to calculate the compensation command. Where b0 is the control gain of the state-space model, and Δu is the disturbance compensation amount as the compensation command; The duty cycle signal is generated by superimposing the compensation command and the basic adjustment command, as follows: Where u is the duty cycle signal.

8. The DC microgrid stability control method considering constant power load as described in claim 7, characterized in that, The dynamic calculation formula for the control gain is as follows: in, This is the partial derivative of the second derivative of the capacitor voltage with respect to the empty percentage signal. It is determined by the parameters of the Boost type DC-DC converter.

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