Disturbance suppression and stability improvement method for hybrid energy storage

Abstract

A disturbance suppression and stability improvement method for hybrid energy storage. The method comprises: on the basis of Kirchhoff's voltage law and Kirchhoff's current law, obtaining an output voltage expression and an output current expression of a grid-connected converter, and on the basis of the output voltage expression and the output current expression, establishing a balance equation for the grid-connected converter; in order to suppress the inconsistency between the filter inductance and capacitance of the grid-connected converter and the magnitudes of designed parameters, setting as a fixed disturbance a current disturbance generated by hardware parameter deviations of the grid-connected converter, and modifying the balance equation for the grid-connected converter into a balance equation including the current disturbance, and a nominal model for a filter loop voltage of the grid-connected converter within one cycle; and in order to implement tracking of a reference voltage by a voltage that is output by the nominal model, and on the basis of a sliding mode function, using a dual-power sliding-mode compensation controller based on a variable speed reaching law, and calculating the first-order derivative of a sliding mode surface, and applying sliding mode control to a voltage control system of a hybrid energy storage converter, thus realizing voltage steady-state control.

Description

Hybrid energy storage disturbance suppression stability improvement method

[0001] The present application claims priority to the Chinese patent application No. 202410436504.1, filed on April 11, 2024, and entitled "Hybrid energy storage disturbance suppression stability improvement method", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0002] The present application belongs to the technical field of hybrid energy storage, and specifically relates to a hybrid energy storage disturbance suppression stability improvement method. BACKGROUND

[0003] In order to ensure voltage stability when hybrid energy storage is connected to the grid, voltage control strategies are often used in hybrid energy storage converters. Since the circuit of a hybrid energy storage three-phase converter is a complex system with time-varying, nonlinear, and multi-parameter coupling characteristics, it has become a research hotspot to ensure that the output voltage of the converter has low steady-state tracking error and strong robustness when the hybrid energy storage is connected to the grid.

[0004] When a hybrid energy storage system is connected to the grid, it is crucial to maintain voltage stability. Therefore, voltage control strategies are often used in hybrid energy storage converters to achieve stable voltage output. However, the circuit structure of a hybrid energy storage three-phase converter is very complex, with time-varying, nonlinear, and multi-parameter coupling characteristics. This means that the operation of the converter is affected by multiple factors, and these factors interact with each other, making control more challenging.

[0005] To address this issue, in order to ensure that the hybrid energy storage system can output stable and accurate voltage when connected to the grid, the converter must not only have a small steady-state tracking error, i.e., the voltage output should have minimal fluctuations during long-term operation, but also have strong robustness, i.e., it should be able to cope with various uncertain factors such as system parameter changes and external disturbances, and maintain voltage output stability. Therefore, how to design an effective control strategy to make the converter perform well in complex operating environments has become a hot and difficult research topic.

[0006] SUMMARY

[0007] The present application aims to address the shortcomings of the prior art and provides a hybrid energy storage disturbance suppression stability improvement method.

[0008] The present application is implemented by adopting the following technical solutions:

[0009] A hybrid energy storage disturbance suppression stability improvement method based on a hybrid energy storage converter voltage control system, the system including supercapacitors and lithium-ion batteries, the method comprising:

[0010] S1: According to the Kirchhoff voltage and current law, the grid-connected converter output voltage and output current expression, and according to the output voltage and output current expression, the grid-connected converter balance equation is established;

[0011] S2: In order to suppress the inconsistency between the filter inductance and capacitance of the grid-connected converter and the designed parameter size, the current disturbance generated by the hardware parameter deviation of the grid-connected converter is set as a fixed disturbance, the grid-connected converter balance equation is rewritten as a balance equation containing the current disturbance and a nominal model of the filter loop voltage within one cycle of the grid-connected converter;

[0012] S3: In order to realize the tracking of the voltage output by the nominal model to the reference voltage, based on the sliding mode function, a double-power variable speed approaching double-power sliding mode compensation controller is adopted, and the first derivative of the sliding surface is calculated, and the sliding mode control is applied to the voltage control system of the hybrid energy storage converter, thereby realizing the voltage steady-state control.

[0013] The further improvement of the application is that the grid-connected converter output voltage and output current expression is: The output current expression is substituted into the output voltage to obtain the grid-connected converter balance equation, which is expressed as: The Clark transformation is performed on the grid-connected converter balance equation to obtain the αβ coordinate grid-connected converter balance equation:

[0014] Wherein: u inα , u inβ is the neutral point voltage of the grid-connected converter in the αβ coordinate system; u α , u β is the output voltage of the grid-connected converter in the αβ coordinate system; i oα , i oβ is the output current of the grid-connected converter in the αβ coordinate system.

[0015] The further improvement of the application is that, in order to suppress the inconsistency between the filter inductance and capacitance of the grid-connected converter and the designed parameter size, the current disturbance i oα , i oβ generated by the hardware parameter deviation of the grid-connected converter is set as a fixed disturbance, and the αβ coordinate grid-connected converter balance equation is rewritten as:

[0016] The current disturbance i oα , i oβ in the above formula is set as a fixed disturbance of 0, and the filter inductance deviation ΔL f = 0, the filter capacitance deviation ΔC f = 0, and the nominal model of the filter loop voltage within one cycle of the grid-connected converter is obtained as:

[0017] Wherein: J n = L f C f , B n = C f R f To establish the nominal model inductance capacitance parameter; u n = [u α u β ] T ; u in = [u inα u inβ ] T .

[0018] The further improvement of the application is that in the control strategy based on the nominal model, for the alpha axis, the nominal model voltage tracking error e1 = u n -u ref is defined, u n is brought into the nominal model of the filter circuit voltage of the grid-connected converter in one cycle, and the nominal model of the filter circuit voltage of the grid-connected converter in one cycle containing the voltage tracking error is obtained as follows: The control rate u in of the nominal model is set as follows:

[0019] Wherein: k1, k2 are control parameters, and k1>0, k2>0.

[0020] The further improvement of the application is that the control rate u in of the nominal model is brought into the nominal model of the filter circuit voltage of the grid-connected converter in one cycle containing the voltage tracking error, and the nominal model of the filter circuit voltage of the grid-connected converter in one cycle containing the control rate of the nominal model is obtained as follows: In order to make the second-order system stable, the system stability relationship σ 2 +(k2+B n / J n )σ+k1=0 needs to be met; wherein: σ is the Laplace operator.

[0021] The further improvement of the application is that the real part of the eigenvalue of the system stability relationship σ 2 +(k2+B n / J n )σ+k1=0 is negative, (σ+h) 2 =0, h>0, then σ 2 +2hσ+h 2 =0; wherein: h is a dynamic performance index, and when the real part of the eigenvalue thereof is negative, the following corresponding relationship is met: By determining the value of h, k1, k2 are determined, the dynamic performance index meeting the requirements is determined, and the tracking of the voltage output by the nominal model to the reference voltage is realized.

[0022] The further improvement of the application is that the sliding mode function s is defined as: Wherein: e2 is the sliding mode function voltage tracking error, e2=u-u n ; The derivative of e2 is d; c is the integral coefficient of the sliding mode function; t is the upper limit of the integral of the sliding mode function; tau is the current time of the integral of the sliding mode function.

[0023] The further improvement of the application is that the first derivative of the sliding surface is obtained, that is, the derivative of the sliding mode function s, and the first derivative of the sliding surface is represented as: In view of the problems of single speed and slow dynamic response of the traditional power law, a double power variable speed approaching double power sliding mode compensation controller is adopted, the chattering existing in the sliding mode control is reduced through the double power law, and the robustness of the inverter system is improved; the first derivative of the sliding surface is represented as:

[0024] Wherein: e1e λG(s) |s| δ Sgn(s) is a power variable term; e is an exponential function; lambda is an adjustment parameter; e1, e2 are double power function first coefficients; delta, eta are power coefficients; η Sgn(s) is an equivalent constant term; e1, e2 are double power function first coefficients; delta, eta are power coefficients;

[0025] When s tends to the sliding surface, the approaching speed is ensured not to tend to 0 to reduce the approaching time, and lambda>0, 0<delta<1, eta>1, and the saturation function G(s) is represented as:

[0026] The further improvement of the application is that the nominal model of the filter loop voltage of the grid-connected converter in one period is brought into the first derivative of the sliding surface, and the hybrid energy storage converter sliding mode control equation is obtained as:

[0027] The set energy storage converter sliding mode control is applied to the energy storage converter voltage control system, and then the voltage steady-state control is realized.

[0028] Compared with the prior art, the application has at least the following beneficial technical effects:

[0029] 1. The application introduces an improved sliding mode control strategy for the control problem in the hybrid energy storage converter. The double power variable speed approaching law function is adopted, which effectively solves the problem of too single and slow dynamic response of the traditional approaching law function. The control performance of the hybrid energy storage converter can be significantly improved, and more rapid, stable and accurate energy conversion is realized.

[0030] 2、In order to verify the stability of the double power law sliding mode control compensation law, the second Lyapunov method is used as the theoretical support. By setting a series of dynamic indicators that meet the system performance requirements, the sliding mode control can accurately and effectively regulate and control the voltage. Not only does it ensure the stability of the control strategy, but it also significantly improves the voltage control performance of the hybrid energy storage converter. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 is a circuit diagram of the voltage control system of the hybrid energy storage converter in the embodiment of the present application. DETAILED DESCRIPTION

[0032] The exemplary embodiments of the present application will be described in detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present application are shown in the drawings, it should be understood that the present application can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided so that the present application can be more thoroughly understood and the scope of the present application can be accurately conveyed to those skilled in the art. It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments.

[0033] As shown in Figure 1, the hybrid energy storage is composed of supercapacitors and lithium ion batteries, and the supercapacitors and lithium ion batteries have x grid-connected converters in common. Among them, U dc,x is the DC side voltage of the xth grid-connected converter; i Labc,x , i oabc,x are the output current of the grid-connected converter and the current at the point of common coupling, respectively; n is the neutral point of the grid-connected converter; N is the reference potential of the grid-connected converter voltage; u nN is the potential voltage drop from the load neutral point to the reference point, which can be expressed as: u nN = (u aN + u bN + u cN ) / 3, where: u aN , u bN , u cN are the a, b, c three-phase voltages of the grid-connected converter; R f,x , L f,x , C f,x are the parasitic resistance, filter inductance and filter capacitance in the LC filter, respectively; R line,x , L line,x are the line impedance and reactance of the grid-connected converter, respectively; u pcc is the AC bus voltage. The grid-connected converters used in the present application have the same capacity, and grid-connected converter 1 is taken as the research object and its subscript 1 is ignored.

[0034] According to the Kirchhoff voltage and current law, the grid-connected converter output voltage is expressed as:

[0035] The grid-connected converter output current is expressed as:

[0036] Substituting equation (2) into equation (1), the grid-connected converter balance equation can be expressed as:

[0037] The Clark transformation is applied to equation (3), and the αβ coordinate grid-connected converter balance equation is obtained as:

[0038] In the equation: u inα , u inβ is the neutral point voltage of the grid-connected converter in the αβ coordinate system; u α , u β is the grid-connected converter output voltage in the αβ coordinate system; i oα , i oβ is the grid-connected converter output current in the αβ coordinate system.

[0039] However, in actual operation, the filter inductance and capacitance of the grid-connected converter do not match the designed parameters, and the super capacitor and lithium ion battery have different front-end discharge characteristics, causing the grid-connected converter to have circulating current. This part of the current can be regarded as disturbance, which ultimately affects the balance of the grid-connected converter output voltage. In this application, the current disturbance i oα , i oβ generated by the hardware parameter deviation of the grid-connected converter is set as the inherent disturbance, and equation (4) can be rewritten as:

[0040] The current disturbance i oα , i oβ in equation (5) is set as 0, and the filter inductance deviation ΔL f = 0, the filter capacitance deviation ΔC f = 0, and the nominal model of the filter circuit voltage within one period of the grid-connected converter is obtained as:

[0041] In the equation: J n = L f C f , B n = C f R f is the inductance and capacitance parameter for establishing the nominal model; u n = [u α u β ] T ; uin = [u inα u inβ ] T .

[0042] In the control strategy based on the nominal model, the application of the conventional reference instruction is different, the nominal model and the actual voltage reference input obtained by the droop control link are all derived from the nominal model controller. For the sake of clarity of subsequent discussion, the following will take the α axis as an example for detailed analysis and discussion.

[0043] Define the nominal model voltage tracking error e1 = u n -u ref , u n = -k1e1-k2e1 (6)

[0044] In formula (7), the control rate u in of the nominal model set by the present application is:

[0045] In the formula: k1, k2 are control parameters, which need to be set as k1>0, k2>0.

[0046] Bring formula (8) into formula (7), we can get:

[0047] In order to ensure the stability of the above-mentioned second-order system, it is necessary to meet: σ 2 +(k2+B n / J n )σ+k1=0 (10)

[0048] In the formula: σ is the Laplace operator.

[0049] To meet the characteristic value of σ 2 +(k2+B n / J n )σ+k1=0 is negative, the present application takes (σ+h) 2 =0, h>0, then σ 2 +2hσ+h 2 =0. Wherein: h is a dynamic performance index, which meets the characteristic value of the real part is negative, then there is the following corresponding relationship:

[0050] By determining the value of h, k1 and k2 can be determined, which can meet the required dynamic performance index and realize the tracking of the voltage output by the nominal model to the reference voltage.

[0051] Define the sliding mode function s as:

[0052] Where: e2 is the sliding mode function voltage tracking error, e2=uu n ; is the derivative of e2; c is the integral coefficient of the sliding mode function; t is the upper limit of the integral of the sliding mode function; τ is the current moment of the integral of the sliding mode function.

[0053] Find the first derivative of the sliding surface:

[0054] To address the problems of the traditional power-law reaching law with a single speed and slow dynamic response, this application proposes a dual-power variable speed approaching dual-power sliding mode compensation controller. This controller uses the dual-power reaching law to reduce chattering in the sliding mode control and improve the robustness of the inverter system. The first-order derivative of the sliding mode surface can be expressed as:

[0055] Where: ε1e λG(s) |s| δ sgn(s) is the power speed change term; e is the exponential function; λ is the adjustment parameter; ε|s| η sgn(s) is an equivalent constant; ε1 and ε2 are the linear coefficients of the double power function; δ and η are the power coefficients. When s approaches the sliding surface, the approach velocity is guaranteed not to approach zero, thus reducing the approach time. Furthermore, λ > 0, 0 < δ < 1, and η > 1. The saturation function G(s) can be expressed as:

[0056] Where: Δ is the set boundary.

[0057] Substituting equation (6) into equation (14), the sliding mode control equation of the energy storage converter can be obtained as follows:

[0058] Applying the above-set energy storage converter sliding mode control to the energy storage converter voltage control system can achieve voltage steady-state control.

[0059] Although the present application has been described in detail above using general descriptions and specific embodiments, it will be apparent to those skilled in the art that modifications or improvements may be made based on the present application. Therefore, such modifications or improvements, which do not depart from the spirit of the present application, are within the scope of protection claimed in the present application.

Claims

1. A method for improving the stability of hybrid energy storage disturbance suppression, characterized in that: The method is based on a hybrid energy storage converter voltage control system, which includes a supercapacitor and a lithium-ion battery. The method includes: S1: Based on Kirchhoff's voltage and current laws, the grid-connected converter output voltage and output current expressions are obtained, and the grid-connected converter balance equation is established based on the output voltage and output current expressions; S2: To suppress the inconsistency between the filter inductance and capacitance of the grid-connected converter and the designed parameters, the current disturbance caused by the hardware parameter deviation of the grid-connected converter is set as a fixed disturbance. The grid-connected converter balance equation is rewritten to include the current disturbance and the nominal model of the filter circuit voltage within one cycle of the grid-connected converter. S3: In order to achieve the tracking of the nominal model output voltage to the reference voltage, a double-power variable speed approach to double-power sliding mode compensation controller is adopted based on the sliding mode function, and the first-order derivative of the sliding mode surface is calculated. The sliding mode control is applied to the voltage control system of the hybrid energy storage converter to achieve voltage steady-state control.

2. The hybrid energy storage disturbance suppression stability improvement method according to claim 1 is characterized in that: The output voltage and output current of the grid-connected converter are expressed as follows: Substituting the output current expression into the output voltage, the grid-connected converter balance equation is obtained as follows: By performing Clark transformation on the grid-connected converter balance equation, the grid-connected converter balance equation in αβ coordinates can be obtained as follows: Where: u inα 、u inβ is the neutral point voltage of the grid-connected converter in the αβ coordinate system; u α 、u β is the output voltage of the grid-connected converter in the αβ coordinate system; i oα 、i oβ is the output current of the grid-connected converter in the αβ coordinate system.

3. The hybrid energy storage disturbance suppression stability improvement method according to claim 2 is characterized in that: In order to suppress the inconsistency between the filter inductance and capacitance of the grid-connected converter and the designed parameters, the current disturbance i generated by the hardware parameter deviation of the grid-connected converter is converted to oα 、i oβ Assuming it is a fixed disturbance, the αβ coordinate grid-connected converter balance equation is rewritten as: Assume the current disturbance i in the above formula oα 、i oβ Assume that the inherent disturbance is 0 and the filter inductance deviation VL f =0, filter voltage deviation VC f =0, the nominal model of the filter circuit voltage in one cycle of the grid-connected converter is: Among them: J n =L f C f 、B n =C f R f To establish the nominal model inductor and capacitor parameters; in n =[in α in β ] T ;in in =[in inα in inβ ] T 。 4. The hybrid energy storage disturbance suppression stability improvement method according to claim 3 is characterized in that: In the control strategy based on the nominal model, for the α axis, the nominal model voltage tracking error e1 = u n -u ref , will u n Substituting this into the nominal model of the filter circuit voltage within one cycle of the grid-connected converter, the nominal model of the filter circuit voltage within one cycle of the grid-connected converter with voltage tracking error is obtained as follows: Set the control rate u of the nominal model in for: Among them: k1, k2 are control parameters, and k1>0, k2>0.

5. The hybrid energy storage disturbance suppression stability improvement method according to claim 4 is characterized in that: The control rate u of the nominal model will be set in Substituting the nominal model of the filter circuit voltage of the grid-connected converter within one cycle with the voltage tracking error, the nominal model of the filter circuit voltage of the grid-connected converter within one cycle with the control rate of the nominal model is obtained as follows: In order to make the second-order system stable, the system stability relationship needs to be satisfied: 2 +(k2+B n / J n )σ+k1=0; where: σ is the Laplace operator.

6. The hybrid energy storage disturbance suppression stability improvement method according to claim 5 is characterized in that: System stability relation σ 2 +(k2+B n / J n )σ+k1=0 eigenvalue real part is negative, take (σ+h) 2 =0,h>0, then σ 2 +2hσ+h 2 =0; In the equation: h is a dynamic performance index. If the real part of its eigenvalue is negative, then the following corresponding relationship exists: By determining the value of h, k1 and k2 are determined to meet the required dynamic performance indicators and achieve the tracking of the nominal model output voltage to the reference voltage.

7. The hybrid energy storage disturbance suppression stability improvement method according to claim 6 is characterized in that: The sliding mode function s is defined as: Where: e2 is the sliding mode function voltage tracking error, e2=uu n ; is the derivative of e2; c is the integral coefficient of the sliding mode function; t is the upper limit of the integral of the sliding mode function; τ is the current moment of the integral of the sliding mode function.

8. The hybrid energy storage disturbance suppression stability improvement method according to claim 7 is characterized in that: Find the first-order derivative of the sliding surface, that is, find the derivative of the sliding function s. The first-order derivative of the sliding surface is expressed as: To address the problems of single speed and slow dynamic response of the traditional power-law approach, a dual-power variable speed approach dual-power sliding mode compensation controller is adopted. The dual-power reaching law is used to reduce the chattering in the sliding mode control and improve the robustness of the inverter system. The first-order derivative of the sliding mode surface is expressed as: Where: ε1e λG(s) |s| δ sgn(s) is the power speed change term; e is the exponential function; λ is the adjustment parameter; ε|s| η sgn(s) is an equivalent constant term; ε1 and ε2 are the first-order coefficients of the double power function; δ and η are the power coefficients; When s approaches the sliding surface, the approach velocity is guaranteed not to approach 0 and the approach time is reduced, and λ>0, 0<δ<1, η>1, the saturation function G(s) is expressed as:

9. The hybrid energy storage disturbance suppression stability improvement method according to claim 8 is characterized in that: Substituting the nominal model of the filter circuit voltage in one cycle of the grid-connected converter into the first-order derivative of the sliding mode surface, the sliding mode control equation of the hybrid energy storage converter is obtained as follows: The set energy storage converter sliding mode control is applied to the energy storage converter voltage control system to achieve voltage steady-state control.

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