AHO-based nonlinear droop control method for energy storage bidirectional DC / DC converter
By using AHO-based nonlinear droop control of the bidirectional DC/DC converter for energy storage and optimizing the equivalent droop coefficient, the problems of insufficient bus voltage deviation and heavy-load output power distribution accuracy in DC microgrids are solved, achieving more stable voltage and power regulation.
Patent Information
- Application Number
- CN202511538451.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-10-27
- Publication Date
- 2026-02-13
AI Technical Summary
Traditional droop control in DC microgrids suffers from problems such as insufficient accuracy in bus voltage deviation and heavy-load output power distribution, and its control effect is particularly poor during communication failures.
A nonlinear droop control method based on AHO for energy storage bidirectional DC/DC converters is adopted. By designing a first-order nonlinear autonomous system, the output current and parameters are introduced, and the equivalent droop coefficient is optimized to achieve dynamic adjustment of output voltage and power.
It reduces DC bus voltage deviation, improves the accuracy of heavy-load output power distribution, reduces voltage transient fluctuations, and enhances system stability and reliability.
Smart Images
Figure CN121529487A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The application belongs to the technical field of energy storage converter control, and particularly relates to a nonlinear droop control method for an energy storage bidirectional DC / DC converter based on AHO. BACKGROUND
[0002] With the development of renewable energy, DC microgrid as an important way to accommodate distributed renewable energy has been widely concerned. However, the randomness and uncertainty of renewable energy will reduce the performance of the whole system and have a great impact on power supply quality. In order to suppress the power fluctuation in the grid and improve the reliability of power supply, the addition of energy storage devices has become an effective way to realize the stable operation of DC microgrid. In actual engineering application, multiple energy storage units are connected in parallel to the DC bus of the DC microgrid. Therefore, in order to realize the coordination of sources, storages and loads and achieve power balance, effective control strategies are needed to ensure the stability of the DC bus voltage and the coordinated control of the output power of multiple parallel energy storage bidirectional DC / DC converters.
[0003] Droop control is widely used in energy storage bidirectional DC / DC converters in DC microgrid due to its "plug and play, no communication" advantage, which improves the power distribution accuracy error caused by line impedance. However, the traditional droop control has limitations: a too large droop coefficient can improve the power sharing accuracy, but it will cause a large bus voltage deviation; a too small droop coefficient will reduce the bus voltage deviation, but the output power sharing accuracy is poor, and in heavy load conditions, it may cause the energy storage bidirectional DC / DC converter to overload, leading to system failure. To solve this problem, traditional methods mostly use centralized secondary control and distributed secondary control based on communication links to achieve bus voltage compensation and power distribution, but when communication failure occurs, the control effect is not good and the reliability is relatively poor.
[0004] In order to save communication links and improve the limitations of traditional droop control, nonlinear droop control is proposed. Currently, the application scenarios of nonlinear droop control research are mainly for power unidirectional flow distributed power interface converters, and there are few related researches on energy storage bidirectional DC / DC converters. Most nonlinear droop controls only focus on the steady-state droop curve design within the rated power range and do not consider the dynamic regulation ability of the output voltage of the energy storage bidirectional DC / DC converter. Therefore, further research is needed on the design and application of nonlinear droop control in energy storage bidirectional DC / DC converters and the dynamic regulation of output voltage. SUMMARY
[0005] The purpose of the present application is to provide a nonlinear droop control method for an energy storage bidirectional DC / DC converter based on AHO, which not only reduces the DC bus voltage deviation, but also improves the heavy load output power sharing accuracy, making the DC bus voltage more stable.
[0006] The technical scheme adopted by the present application is a nonlinear droop control method for a DC micro-grid energy storage bidirectional DC / DC converter based on AHO, which is specifically performed according to the following steps: Step 1, a first-order nonlinear autonomous system is designed with reference to AHO characteristics; Step 2, the output current and parameters of the energy storage bidirectional DC / DC converter are introduced into the first-order nonlinear autonomous system, and a nonlinear droop control applied to the energy storage bidirectional DC / DC converter is designed.
[0007] The present application is also characterized in that, In step 1, the state differential equation matrix of AHO is established, the state variables of the state differential equation matrix are derived, the output voltage of the energy storage bidirectional DC / DC converter U and the rated voltage of the DC bus U 0 are respectively corresponding to the resultant vector in the derived formula, and the expression of the first-order nonlinear autonomous system is obtained. Specifically, Step 1.1, the state differential equation matrix of AHO is established, as shown in formula (1): (1); In formula (1), , are the first-order derivatives with respect to time, x the resultant vector of the state variables and , the modulus of x , the capacitor voltage, the inductor current, , L the inductor parameter, C the capacitor parameter, the resonant frequency, the speed parameter for determining the state variables of AHO to tend to be stable, X nom the set effective value of the resultant vector x ; The state variables of formula (1) are derived to obtain formula (2): (2); In formula (2), is x the first-order derivative with respect to time; Step 1.2, the output voltage of the energy storage bidirectional DC / DC converter U and the rated voltage of the DC bus U 0 are respectively corresponding to x and Correspondingly, the first-order nonlinear autonomous system expression is obtained, as shown in formula (3): (3); In formula (3), U Vout is the output voltage of the energy storage bidirectional DC / DC converter, is U the first-order derivative with respect to time, U 0 is the rated voltage of the DC bus, m is the influence of the speed parameter tending to be stable.
[0008] In step 2, according to the first-order autonomous system of the output voltage of the energy storage bidirectional DC / DC converter, the output current k of the energy storage bidirectional DC / DC converter is introduced, and the output voltage-output current relationship is obtained; a steady-state operating point is selected, and a pair of small signal disturbances are superimposed to obtain the equivalent droop coefficient expression. Specifically: Step 2.1, according to the first-order autonomous system of the output voltage of the energy storage bidirectional DC / DC converter, the output current k of the energy storage bidirectional DC / DC converter is introduced, and the output voltage-output current relationship is obtained as shown in formula (4): (4); In formula (4), I Iout is the output current of the energy storage bidirectional DC / DC converter, k is a constant, n is a parameter that determines the nonlinear droop control voltage range; Step 2.2, when the energy storage bidirectional DC / DC converter adopts AHO nonlinear droop control, at steady state, , formula (5) can be obtained by substituting formula (4): (5); In formula (5), P Pout is the output power of the energy storage bidirectional DC / DC converter; Step 2.3, in formula (5), a steady-state operating point and are selected, a pair of small signal disturbances are superimposed, and the equivalent droop coefficient expression is obtained as shown in formula (7): (7); In formula (7), is the steady-state voltage value, is the steady-state output power value, is the voltage small signal disturbance added, is the output power small signal disturbance added; K eqThe equivalent droop coefficient of the steady-state operating point of the nonlinear droop control.
[0009] The AHO-based nonlinear droop control of the energy storage bidirectional DC / DC converter of the direct current micro-grid can reduce the bus voltage deviation and improve the accuracy of the output power sharing under heavy load, and can reduce voltage transient fluctuation by adjusting the output voltage dynamic response through parameters under the charge-discharge switching working condition, compared with the traditional P-U droop control in the energy storage bidirectional DC / DC converter interconnected system considering line impedance. BRIEF DESCRIPTION OF DRAWINGS
[0010] Figure 1 It is a structure diagram of the AHO-based nonlinear droop control system of the energy storage bidirectional DC / DC converter of the present application. Figure 2 It is a time domain simulation diagram of the first-order nonlinear autonomous system with different initial values in the AHO-based nonlinear droop control of the energy storage bidirectional DC / DC converter of the present application. Figure 3 It is a time domain simulation diagram of the first-order nonlinear autonomous system with the same initial value in the AHO-based nonlinear droop control of the energy storage bidirectional DC / DC converter of the present application. Figure 4 It is a nonlinear droop curve and a traditional P-U droop curve diagram of the method of the present application under different k values. Figure 5 It is an equivalent droop coefficient diagram of the method of the present application. Figure 6 It is a simplified direct current micro-grid simulation architecture diagram of the method of the present application. Figure 7 It is a comparison diagram of the direct current bus voltage simulation waveform of the method of the present application and the traditional P-U droop control charge-discharge switching under heavy load. Figure 8 It is a comparison diagram of the output power simulation waveform of the energy storage bidirectional DC / DC converter of the method of the present application and the traditional P-U droop control charge-discharge switching under heavy load. DETAILED DESCRIPTION
[0011] The present application will be described in detail below in combination with the drawings and specific embodiments.
[0012] Embodiment 1 The AHO-based nonlinear droop control system of the energy storage bidirectional DC / DC converter of the present application, as shown in Figure 1 , includes two parts of the bidirectional DC / DC converter topological circuit and its control circuit. Among them, U b is the battery end voltage, L is the inductance in the converter, ri Z is the line impedance, I Li and I i respectively the battery output current and the converter output current, C is the output capacitor, U i is the output voltage. The specific structure of the topology circuit is: the left side is connected with the battery, the middle part switches the current direction through two switch tubes of the same bridge arm (i.e. S 1 is turned on S 2 is turned off, the energy flows from the battery to the bus side; S 2 is turned on S 1 is turned off, the energy flows from the bus side to the battery), and the right side converter output passes through the voltage stabilizing capacitor C through the line impedance r i is connected to the DC bus; The basic working principle of the bidirectional DC / DC converter is that when the DC bus voltage is higher than the rated voltage U 0, it indicates that the system power is excessive, at this time the switch tube S 1 is closed, S 2 is turned on, the battery is charged, that is, the excess power on the DC side is output; when the DC bus voltage is lower than U 0, it indicates that the system power is insufficient, at this time the switch tube S 2 is closed, S 1 is turned on, the battery is discharged, that is, power is provided for the DC side; The specific control block diagram of the control circuit is shown in Figure 1 , which is specifically, the output current I i of the energy storage bidirectional DC / DC converter is sampled, and is substituted into the nonlinear droop expression designed by formula (4), and the output voltage reference value U ref is obtained through the integral link. The output voltage U i of the energy storage bidirectional DC / DC converter is sampled, and the difference between it and U ref is obtained through the voltage loop PI controller to obtain the inductor current reference value I ref . After comparison with the inductor current I L , the output obtained through the current loop PI regulation is transmitted to the PWM pulse signal generator to generate a pulse signal to control the turn-on and turn-off of S 1 and S 2, so as to maintain the stability of the DC bus voltage; Example 2 The nonlinear droop control method for bidirectional DC / DC converters based on AHO in DC microgrid energy storage according to the present invention is carried out according to the following steps: Step 1: Design a first-order nonlinear autonomous system based on the AHO characteristics; specifically: Step 1.1: Establish the state differential equation matrix of AHO, as shown in equation (1): (1); In equation (1), , They are respectively The first derivative with respect to time, x State variables and The composite vector, for x The modulus, The voltage across the capacitor. For inductor current, , L For inductance parameters, C For capacitance parameters, The resonant frequency, To determine the velocity parameters that allow AHO's state variables to tend towards steady state, X nom For the synthesized vector x The set valid value; Equation (2) is derived by deriving the state variables of equation (1): (2); In equation (2), for x The first derivative with respect to time; Step 1.2: Convert the output voltage of the energy storage bidirectional DC / DC converter. U and DC bus rated voltage U 0 and equation (2) respectively x and Correspondingly, the expression for the first-order nonlinear autonomous system is obtained, as shown in equation (3): (3); In equation (3), U The output voltage of the energy storage bidirectional DC / DC converter. for U The first derivative with respect to time, U 0 represents the rated voltage of the DC bus. m To influence Velocity parameters that tend towards steady state; Step 2, introducing the output current and parameters of the energy storage bidirectional DC / DC converter into the first-order nonlinear autonomous system, designing the nonlinear droop control applied to the energy storage bidirectional DC / DC converter, specifically: Step 2.1, introducing the output current of the energy storage bidirectional DC / DC converter into the designed first-order autonomous system of the output voltage of the energy storage bidirectional DC / DC converter k power term, obtaining the output voltage-output current relationship as shown in equation (4): (4); In equation (4), I is the output current of the energy storage bidirectional DC / DC converter, k is a constant, n is a parameter that determines the voltage range of the nonlinear droop control; Step 2.2, when the energy storage bidirectional DC / DC converter adopts AHO nonlinear droop control, in the steady state, , substituting equation (4) can obtain equation (5): (5); In equation (5), P is the output power of the energy storage bidirectional DC / DC converter; When the energy storage bidirectional DC / DC converter is in the discharging state, its steady-state DC bus voltage is maximally reduced to 95% of its rated voltage, and similarly, when the energy storage bidirectional DC / DC converter is in the charging state, its steady-state voltage is maximally increased to 105% of the rated voltage, and by switching n value to realize the charging and discharging mode switching of the energy storage bidirectional DC / DC converter, its output voltage and output power meet the set nonlinear droop curve; From equation (5), the expression of the parameter n is equation (6): (6); In equation (6), P 0 is the rated power of the energy storage bidirectional DC / DC converter, n 1 is the value of the energy storage bidirectional DC / DC converter when working in discharging n , n 2 is the value of the energy storage bidirectional DC / DC converter when working in charging n ; Step 2.3, in equation (5), selecting a steady-state operating point and , superimposing a pair of small signal disturbances, obtaining the equivalent droop coefficient expression as shown in equation (7): (7); In equation (7), is a voltage steady-state value, is an output power steady-state value, is a voltage small signal disturbance added, is an output power small signal disturbance added. K eq is an equivalent droop coefficient of the nonlinear droop control steady-state operating point.
[0013] Compared with the traditional P-U droop control, the proposed nonlinear droop control based on AHO for the energy storage bidirectional DC / DC converter in the energy storage bidirectional DC / DC converter grid-connected system can reduce the bus voltage deviation and improve the heavy load output power sharing accuracy, and can reduce the voltage transient fluctuation through parameter adjustment of the output voltage dynamic response in the charging and discharging switching operating condition.
[0014] Embodiment 3 Figure 2 is a time-domain simulation diagram of the first-order nonlinear autonomous system shown in formula (3) with different initial values, wherein the DC bus voltage rated value is taken as 400V, and the initial values of 600V, 500V, 300V, 200V and 100V are set respectively, and the time-domain simulation of the output voltage is obtained, and it can be seen that under different initial values, the system tends to the rated value 400V finally. U 0 is 400V, and the initial values of 600V, 500V, 300V, 200V and 100V are set respectively, and the time-domain simulation of the output voltage is obtained, and it can be seen that under different initial values, the system tends to the rated value 400V finally. Figure 3 is a first-order nonlinear autonomous system shown in formula (3) with the same initial value 100V, and the parameter m is reduced, the time-domain simulation waveform of the output is m is smaller, the speed of the system tending to the steady-state value is slower, and the output voltage of the energy storage bidirectional DC / DC converter can be realized by adjusting m .
[0015] Embodiment 4 Figure 4 is the nonlinear droop curve of the energy storage bidirectional DC / DC converter obtained from formula (5). The output voltage and output power of the energy storage bidirectional DC / DC converter realize the nonlinear droop characteristic, and considering the power bidirectional flow, when k =2 i ( i =1,2…), the voltage and power nonlinear droop curve cannot be extended to the second quadrant, and k =1, the steady-state voltage of the nonlinear droop control in the charging state is higher than that of the traditional droop control, so k =2 i +1( i = 1,2…). Based on kThe output voltage of the energy storage bidirectional DC / DC converter under the nonlinear droop control of the method has a smaller voltage deviation than the traditional droop control.
[0016] Embodiment 5 Figure 5 The equivalent droop coefficient of the energy storage working in the discharging condition is obtained for formula (7), and under heavy load, the droop coefficient of the nonlinear droop control is greater than that of the traditional P-U droop control, therefore, considering the influence of the line impedance, the output power sharing accuracy of the energy storage bidirectional DC / DC converter under the nonlinear droop control based on the AHO of the method is better than that of the traditional P-U droop control, and the overloading of the energy storage converter is prevented.
[0017] Embodiment 6 Figure 6 A simplified DC microgrid simulation system architecture is shown, wherein the photovoltaic side Boost circuit adopts the maximum power point tracking control, and the two parallel energy storage bidirectional DC / DC converters both adopt the nonlinear droop control based on the AHO of the method. The line impedance from the output end of the two energy storage bidirectional DC / DC converters to the load is r 1=0.5Ω, r 2=0.1Ω; U 1, U 2 is the output voltage of the energy storage bidirectional DC / DC converter, R load is the load resistance.
[0018] According to the above analysis, a simulation is built in MATLAB, and the initial photovoltaic output power is P PV 6kW; the load power is P Load 6kW; Firstly, the feasibility of the method in the charging and discharging switching is verified. The photovoltaic output power is kept unchanged. The load power is suddenly changed to 11kW at the simulation time of 0.5s, so that the energy storage is in the charging state. The load power is suddenly changed to 1.5kW at the simulation time of 1s, so that the energy storage is switched to the discharging state in order to meet the power supply of the load. Figure 7 A DC bus voltage waveform diagram caused by the charging and discharging switching of the energy storage bidirectional DC / DC converter due to the load power fluctuation is shown, and it can be seen that, compared with the traditional P-U droop control, the DC bus voltage under the nonlinear droop control based on the AHO of the method has a smaller voltage deviation, i.e., the voltage deviation is smaller, and because the nonlinear droop control based on the AHO of the method has the voltage regulation capability, the transient fluctuation of the voltage is smaller under the power sudden change condition. Figure 8The output power waveform chart of two parallel energy storage bidirectional DC / DC converters, due to the influence of line impedance, leads to different output powers of the energy storage bidirectional DC / DC converters, and the output power sharing precision of the application under the heavy load condition of charging and discharging is higher than that of the traditional P-U droop control.
[0019] The AHO (Andronov-Hopf oscillator)-based nonlinear droop control method of the energy storage bidirectional DC / DC converter of the direct-current microgrid of the application considers the bidirectional power flow of the energy storage bidirectional DC / DC converter and the influence of line impedance, reduces the deviation of the direct-current bus voltage, improves the heavy load output power sharing precision, and enables the direct-current bus voltage to have dynamic adjustment capability, thereby controlling the stability of the direct-current bus voltage.
Claims
1. A nonlinear droop control method for AHO-based DC microgrid energy storage bidirectional DC / DC converter, characterized in that, Specifically, the following steps are taken: Step 1, design a first-order nonlinear autonomous system according to AHO characteristics; Step 2, introduce energy storage bidirectional DC / DC converter output current and parameters into the first-order nonlinear autonomous system, and design nonlinear droop control applied to energy storage bidirectional DC / DC converter.
2. The AHO-based DC microgrid energy storage bidirectional DC / DC converter nonlinear droop control method of claim 1, wherein, In the step 1, the state differential equation matrix of the AHO is established, the state quantity of the state differential equation matrix is derived, the output voltage of the energy storage bidirectional DC / DC converter U and the DC bus rated voltage U 0 respectively correspond to the resultant vector in the derived formula, and a first-order nonlinear autonomous system expression is obtained.
3. The AHO-based DC microgrid energy storage bidirectional DC / DC converter nonlinear droop control method of claim 2, wherein, In step 1, specifically: Step 1.1, establish the state differential equation matrix of AHO, as shown in equation (1): （1）； In formula (1), , are respectively the first order derivative of time, x is a state variable and a resultant vector, is x a modulus value, is a capacitor voltage, is an inductor current, , L is an inductor parameter, C is a capacitor parameter, is a resonance frequency, is a speed parameter that determines the state quantity of the AHO to tend to a steady state, X nom is a set effective value of the resultant vector x . Derive the state quantity of equation (1) to obtain equation (2): （2）； In formula (2), is x first derivative with respect to time; Step 1.2, the output voltage of the energy storage bidirectional DC / DC converter U and the DC bus rated voltage U 0 respectively correspond to the formula (2) x and The first-order nonlinear autonomous system expression is obtained.
4. The AHO-based DC microgrid energy storage bidirectional DC / DC converter nonlinear droop control method of claim 3, wherein, In step 1.2, the expression of the first-order nonlinear autonomous system is as shown in equation (3): （3）； In formula (3), U is the output voltage of the energy storage bidirectional DC / DC converter, U is the first derivative of time, U 0 is the DC bus voltage rating, m is the influence of is the speed parameter tending to steady state. 5. The AHO-based DC microgrid energy storage bidirectional DC / DC converter nonlinear droop control method of claim 4, wherein, In step 2, according to the first-order autonomous system of the energy storage bidirectional DC / DC converter output voltage, the energy storage bidirectional DC / DC converter output current is introduced k The power term is obtained, and the output voltage-output current relationship is obtained; Select a steady-state operating point, superimpose a pair of small signal disturbances, and obtain an equivalent droop coefficient expression.
6. The AHO-based DC microgrid energy storage bidirectional DC / DC converter nonlinear droop control method of claim 5, wherein, In step 2, specifically: Step 2.1, according to the energy storage bidirectional DC / DC converter output voltage first-order autonomous system, the output current of the energy storage bidirectional DC / DC converter is introduced k The power term is obtained, and the output voltage-output current relationship is as shown in formula (4): （4）； In formula (4), I is an output current of the energy storage bidirectional DC / DC converter, k is a constant, n is a parameter for determining a range of the nonlinear droop control voltage; Step 2.2, when the energy storage bidirectional DC / DC converter adopts AHO nonlinear droop control, in steady state, Substituting equation (4) into equation (5), equation (6) can be obtained. （5）； In formula (5), P Pout is the output power of the energy storage bidirectional DC / DC converter; Step 2.
3. In formula (5), select a steady state operating point and , superimpose a pair of small signal perturbations to get the equivalent droop coefficient expression.
7. The AHO-based DC microgrid energy storage bidirectional DC / DC converter nonlinear droop control method of claim 6, wherein, In step 2.3, the equivalent droop coefficient expression is as shown in equation (7): （7）； In formula (7), is the voltage steady state value, is the output power steady state value, is the added voltage small signal perturbation, is the added output power small signal perturbation; K eq is the equivalent droop coefficient of the nonlinear droop control steady state operating point.
8. The AHO-based DC microgrid energy storage bidirectional DC / DC converter nonlinear droop control method of claim 7, wherein, From equation (5) the expression for the parameter n is derived as equation (6): （6）； In equation (6), P 0 represents the rated power of the energy storage bidirectional DC / DC converter. n 1 is an energy storage bidirectional DC / DC converter operating during discharge. n The value of , n 2 is an energy storage bidirectional DC / DC converter operating during charging. n The value of .