Hybrid energy storage system bus voltage fluctuation stabilizing method based on frequency division feedforward

Abstract

The invention discloses a hybrid energy storage system bus voltage fluctuation stabilizing method based on frequency division feedforward, and relates to the technical field of energy storage energy management. The method mainly comprises the following steps: S1, designing a nonlinear disturbance observer, reading disturbance information according to state variables such as bus voltage and the like, and performing frequency division on the disturbance information to serve as a disturbance component of each part of the hybrid energy storage system; and S2, designing a feed-forward function, eliminating system disturbance by using a disturbance observation value through introducing a feed-forward link, and stabilizing the bus voltage. According to the method, system disturbance information is read mainly through a nonlinear disturbance observer and is fed forward into control loops of all parts of the hybrid energy storage system in a frequency division mode, bus voltage oscillation is eliminated, the system operates stably, and the operation efficiency and quality of an electric tractor are improved. The method is suitable for energy optimization management in the fields of electric tractors, electric automobiles and the like, and the response capability and speed of the hybrid energy storage system are improved.

Description

Technical Field

[0001] This invention relates to the field of energy storage management technology, specifically to the design of a method for smoothing bus voltage fluctuations in a hybrid energy storage system based on frequency division feedforward. Background Technology

[0002] Electric tractors use drive motors and batteries instead of internal combustion engines as their power source, resulting in higher driving efficiency, more flexible control methods, and more accurate control precision. They also allow for more flexible and convenient chassis layout, achieving the operational requirements of low noise and zero emissions. In recent years, breakthroughs in battery energy storage, motor drive, and fast charging technologies have laid a solid foundation for the research and development of electric tractors. Furthermore, my country provides strong support for agricultural machinery and new energy in both research and industrialization.

[0003] Electric tractors often encounter situations where high-power loads are connected or disconnected during operation, posing a significant challenge to the control system. Switching between various complex operating conditions can lead to sudden load changes, causing fluctuations in the motor speed and the system's DC bus voltage, affecting stable system operation. Bus voltage oscillations can also impact the electrical system. Therefore, controlling the electric tractor's power source to cope with sudden load changes and smooth bus voltage fluctuations becomes a critical issue.

[0004] Current research on DC voltage fluctuation mitigation techniques encompasses various control methods. Guo Yuanbo et al. applied active disturbance rejection control (ADRC) to the voltage control of PWM rectifiers, achieving rapid DC-side voltage control and alleviating the jitter problem of the current inner loop setpoint. Building upon this, Fang Yun et al. added coupled input, observation error integral, and dynamic scheduling parameters to the extended state observer, proposing an ADRC algorithm based on an improved extended state observer to suppress the impact of load mutation disturbances. Thus, ADRC is relatively mature, but its principle is complex, making stability analysis difficult for complex systems. In contrast, PID control, dominated by voltage and current loops, has a simple structure and has achieved good results in stabilizing voltage. Some researchers have added disturbance feedforward control to PI control to suppress DC bus voltage fluctuations. Wang Chengshan et al. used unbalanced current or power signals as disturbance signals, injecting them into the original control loop via feedforward to improve the system's dynamic response speed and control effect. However, in practical applications, there are many unmeasurable or inaccurately measurable disturbance variables, making feedforward control design difficult. To address this issue, Wang C et al. proposed a nonlinear disturbance observer, which uses information such as the system model, control input, and measurement output to accurately estimate the equivalent disturbance acting on the system, thereby achieving feedforward control. However, with the widespread application of hybrid energy storage systems, system disturbances are divided into high- and low-frequency components, making it difficult for traditional feedforward methods to completely eliminate system disturbances. Summary of the Invention

[0005] This invention provides a control method for smoothing bus voltage fluctuations in a hybrid energy storage system, which is dominated by an observer and frequency-division feedforward. The aim is to inject system disturbances into the respective control loops of the hybrid energy storage system after passing through frequency-division feedforward, thereby eliminating low-frequency and high-frequency disturbances in the system, optimizing traditional PI control, improving the voltage smoothing effect and system response speed, and enabling the system to operate stably.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for smoothing bus voltage fluctuations in a hybrid energy storage system based on frequency division feedforward includes the following steps:

[0008] Step S1: Design a nonlinear disturbance observer to read disturbance information based on state variables such as bus voltage, and then obtain the disturbance components of the corresponding lithium battery and supercapacitor through a frequency division circuit to provide input for feedforward control;

[0009] Step S2: Design a feedforward function suitable for lithium battery and supercapacitor loops. Inject the frequency-divided disturbance information into the corresponding control loop through the feedforward link, and use the disturbance observation value to eliminate system disturbance and stabilize the bus voltage.

[0010] As a further technical solution of the present invention: the specific process of reading system disturbance information in step S1 includes:

[0011] Step S1.1: Analyze the sources of disturbance in the system and determine the objects to be observed;

[0012] Step S1.2: Design a nonlinear disturbance observer to read the disturbance information.

[0013] As a further technical solution of the present invention: Step S1.1 specifically involves: determining the source of disturbance as bus current: the sudden change in load torque of the electric tractor causes a surge in stator current, which in turn causes a sudden increase in bus current, and then causes bus voltage to oscillate. Therefore, the bus current is taken as the source of system disturbance.

[0014] As a further technical solution of the present invention: step S1.2 specifically involves: constructing a nonlinear disturbance observer: establishing a system equation including bus voltage, inductor current, duty cycle, and bus current based on the system topology; constructing the observer equation and introducing intermediate variables; designing the observation function and gain matrix to make the observer converge, thereby obtaining the disturbance observation value of the bus current. .

[0015] As a further technical solution of the present invention: the system equations are obtained based on the system structure topology, specifically:

[0016] (1)

[0017] (2)

[0018] (3)

[0019] (4)

[0020] Where d1 represents the duty cycle of S1 and S2, and d2 represents the duty cycle of S3 and S4. Based on the nonlinear disturbance observer equation, the system equation is assumed to be:

[0021] (5)

[0022] Where X is a state variable. This includes bus voltage and inductor current; u is the control input, i.e., the duty cycle. d represents the disturbance, i.e., the bus current. y represents the output, i.e., the bus voltage. f(X) represents the natural state of the system, i.e., without control input or disturbance. ;g u (X) is the control input matrix. ;g d(X) is the perturbation input matrix. ;

[0023] Next, construct the observer equations:

[0024] (6)

[0025] To eliminate Direct dependency, introducing intermediate variables The observer equation is rewritten as:

[0026] (7)

[0027] in, Let p(X) be the disturbance observation value; p(X) be the observation function to be designed; and L(X) be the interference gain matrix, which must satisfy:

[0028] (8)

[0029] (9)

[0030] Among them, l i Indicates the feedback gain of the observer;

[0031] Define the perturbation estimation error e d (t), then we have the disturbance error equation:

[0032] (10)

[0033] (11)

[0034] when The observer will be convergent, with a time constant. At this point, the interference observer equation for the lithium battery loop is:

[0035] (12)

[0036] The observed and actual values ​​of the disturbance current have the following relationship:

[0037] (13)

[0038] At this point, the object being observed is the DC bus current, i.e., apparent i dc i is the source of system disturbance. dc Includes lithium battery branch i o1 and supercapacitor branch i o2 This indicates that the disturbance source can be divided into two; therefore, when i is obtained dc After dividing the observed values, we obtain feedforward perturbation observations suitable for lithium batteries and supercapacitors;

[0039] (14)

[0040] (15)

[0041] in, This is the cutoff frequency.

[0042] As a further technical solution of the present invention, the specific steps of the frequency division injection feedforward control in step S2 are as follows:

[0043] Step S2.1: Inject feedforward control into the low-frequency loop;

[0044] Step S2.2: Inject feedforward control into the high-frequency loop.

[0045] As a further technical solution of the present invention: step S2.1 specifically includes:

[0046] First, the system expression is written based on the PI control loop of the lithium battery branch:

[0047] (16)

[0048] The first part of the formula reflects the tracking performance of the DC bus voltage to a given voltage reference value; the second part is the disturbance current i. o1 Interference with bus voltage; Part 3 is the low-frequency loop feedforward term introduced in this design;

[0049] Based on the relationship between the actual and observed values ​​of the disturbance current, the coefficients of the expression are designed to eliminate the disturbance current i. o1 Impact on bus voltage;

[0050] First, based on the control loop, the expressions for each coefficient can be written:

[0051] (17)

[0052] (18)

[0053] (19)

[0054] By canceling out the second and third parts, we can obtain the expression for the low-frequency loop feedforward function:

[0055] (20)

[0056] This theoretically solves the problem of i. o1 For u dc The impact.

[0057] As a further technical solution of the present invention: step S2.2 specifically includes:

[0058] First, the system expression is written based on the PI control loop of the lithium battery branch:

[0059] (twenty one)

[0060] The first part of the formula reflects the tracking performance of the DC bus voltage to a given voltage reference value; the second part is the disturbance current i. o2 Interference with bus voltage; Part Three is the high-frequency loop feedforward term introduced in this design;

[0061] Based on the relationship between the actual and observed values ​​of the disturbance current, the coefficients of the expression are designed to eliminate the disturbance current i. o1 The impact on bus voltage; firstly, based on the control loop, the expressions for each coefficient can be written:

[0062] (twenty two)

[0063] (twenty three)

[0064] (twenty four)

[0065] By canceling out the second and third parts, we can obtain the expression for the high-frequency loop feedforward function:

[0066] (25)

[0067] At this point, the disturbance current i dc Includes i o1 and i o2 Both disturbance components were completely eliminated, theoretically resolving the DC bus voltage u issue. dc Disturbance factors.

[0068] Compared with the prior art, the beneficial effects of the present invention are:

[0069] This invention uses a nonlinear disturbance observer to read system disturbance information and feeds it forward at different frequencies into the control loops of various parts of the hybrid energy storage system. This eliminates bus voltage oscillations, stabilizes the system, and improves the efficiency and quality of electric tractor operations. This invention is applicable to energy optimization management in fields such as electric tractors and electric vehicles, improving the response capability and speed of hybrid energy storage systems. Attached Figure Description

[0070] Figure 1 This is the frequency division feedforward optimization control loop diagram;

[0071] Figure 2 This is a topology diagram of a hybrid energy storage system.

[0072] Figure 3 This is a comparison chart of actual and observed bus current.

[0073] Figure 4 This is a graph showing the frequency division results of the disturbance observations;

[0074] Figure 5 This is a comparison chart of the bus voltage stabilization effect;

[0075] Figure 6 This is a waveform diagram of the bus voltage spike (a).

[0076] Figure 7 This is the waveform diagram of the bus voltage spike (b).

[0077] Figure 8 This is a waveform diagram of the bus voltage spike (c).

[0078] Figure 9 This is a waveform diagram of the bus voltage spike. Detailed Implementation

[0079] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0080] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the invention. Techniques, methods, and apparatus known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and apparatus should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values.

[0081] like Figure 1-9 As shown, the present invention proposes a method for smoothing bus voltage fluctuations in a hybrid energy storage system based on frequency division feedforward. The specific method is as follows:

[0082] Step S1: Design a nonlinear disturbance observer to read disturbance information based on state variables such as bus voltage, and then obtain the disturbance components of the corresponding lithium battery and supercapacitor through a frequency division circuit to provide input for feedforward control;

[0083] Step S2: Design a feedforward function suitable for lithium battery and supercapacitor loops. Inject the frequency-divided disturbance information into the corresponding control loop through the feedforward link, and use the disturbance observation value to eliminate system disturbance and stabilize the bus voltage.

[0084] The specific steps for obtaining the observation system disturbance information in step S1 are as follows:

[0085] Step S1.1: Analyze the sources of disturbance in the system and determine the objects to be observed.

[0086] The constantly changing external operating conditions of electric tractors can cause sudden changes in the torque demand of the load motor. These sudden changes in motor torque lead to a surge in stator current, which in turn causes a surge in bus current. To replenish the bus current output in a timely manner, the voltage stabilizing capacitor also provides energy to the DC bus, resulting in a voltage drop and voltage oscillation. This indicates that the bus current is always a key intermediate variable in the process of external environmental factors causing system bus voltage oscillations. Therefore, this study uses the bus current as the source of system disturbance and designs a nonlinear disturbance observer to read the disturbance of the bus current, aiming to provide a foundation for system control design.

[0087] Step S1.2: Design a nonlinear disturbance observer to read the disturbance information.

[0088] It is known that the oscillation of the bus voltage is caused by disturbances in the system. Therefore, it is necessary to extract the disturbance information and design a control loop to eliminate the disturbance and keep the bus voltage stable. In reality, there are many unmeasurable or inaccurately measurable disturbance variables, which makes the control loop design difficult and the control effect less than ideal. To address this, this study introduces a nonlinear disturbance observer to read the disturbance information. As shown in step S1.1, the bus current is taken as the observation object in this study.

[0089] First, based on the system structure topology, such as... Figure 2 As shown, the system equations are obtained:

[0090] (1)

[0091] (2)

[0092] (3)

[0093] (4)

[0094] Where d1 represents the duty cycle of S1 and S2, and d2 represents the duty cycle of S3 and S4. Based on the nonlinear disturbance observer equation, the system equation is assumed to be:

[0095] (5)

[0096] Where X is a state variable. This includes bus voltage and inductor current; u is the control input, i.e., the duty cycle. d represents the disturbance, i.e., the bus current, d(t) = i dc ; y represents the output, i.e., the bus voltage, y = x1; f(X) represents the natural state of the system, i.e., without control input or disturbance. ;g u (X) is the control input matrix. ;g d (X) is the perturbation input matrix. .

[0097] Next, construct the observer equations:

[0098] (1)

[0099] To eliminate Direct dependency, introducing intermediate variables The observer equation is rewritten as:

[0100] (2)

[0101] in, Let p(X) be the disturbance observation value; p(X) be the observation function to be designed; and L(X) be the interference gain matrix, which must satisfy:

[0102] (8)

[0103] (9)

[0104] Among them, l i This represents the feedback gain of the observer.

[0105] Define the perturbation estimation error e d (t), then we have the disturbance error equation:

[0106] (10)

[0107] (11)

[0108] when The observer will be convergent, with a time constant. To simplify the design, while ensuring convergence, we can choose l1<0, l2=0, l3=0, then the time constant T=-(C1+C2) / l1. In this case, the interference observer equation for the lithium battery loop is:

[0109] (12)

[0110] When selecting l1, care should be taken to avoid implementation difficulties caused by excessively large values, such as saturation effects and increased noise. It is generally desirable for the observer's response speed to be faster than that of the feedback control system. The observed and actual values ​​of the disturbance current have the following relationship:

[0111] (13)

[0112] Simulation experiments can compare the actual value of the bus current with the observed value, such as... Figure 3 As can be seen, the observation results are quite good. The object being observed at this time is the DC bus current, i.e., apparent i. dc i is the source of system disturbance. dc Includes lithium battery branch i o1 and supercapacitor branch i o2 This indicates that the disturbance source can be divided into two. Therefore, after obtaining i dc After obtaining the observations, they need to be frequency-divided to obtain feedforward perturbation observations suitable for lithium batteries and supercapacitors.

[0113] (14)

[0114] (15)

[0115] in, The cutoff frequency is used. The perturbation components after frequency division can be plotted through simulation experiments as follows: Figure 5 .

[0116] The specific steps of the frequency division injection feedforward control described in step S2 are as follows:

[0117] Step S2.1: Inject feedforward control into the low-frequency loop.

[0118] Step S1 completes the observation of the system disturbance, obtaining the input quantity for feedforward control. The purpose of feedforward is to eliminate the influence of the disturbance on the system output by injecting the observed value of the disturbance signal into the control loop through a feedforward function. Because the system is affected by i o1 and i o2 The interference from the two disturbance terms necessitates the design of feedforward functions for the low-frequency and high-frequency control loops, corresponding to lithium batteries and supercapacitors respectively.

[0119] First, write the system expression based on the PI control loop of the lithium battery branch:

[0120] (16)

[0121] The first part of the formula reflects the tracking performance of the DC bus voltage to a given voltage reference value; the second part is the disturbance current i.o1 The interference with the bus voltage; the third part is the low-frequency loop feedforward term introduced in this design. Based on the previous analysis, it is necessary to design the coefficients of the expression based on the relationship between the actual and observed values ​​of the disturbance current, and to eliminate the disturbance current i. o1 The impact on bus voltage. First, based on the control loop, the expressions for each coefficient can be written:

[0122] (17)

[0123] (18)

[0124] (19)

[0125] The transfer function in the coefficient expression can be obtained through small-signal modeling. By canceling out the second and third parts, the expression for the low-frequency loop feedforward function can be obtained as follows:

[0126] (20)

[0127] This theoretically solves the problem of i. o1 For u dc The impact.

[0128] Step S2.2: Inject feedforward control into the high-frequency loop.

[0129] The system expression is first written based on the PI control loop of the supercapacitor branch:

[0130] (twenty one)

[0131] The first part of the formula reflects the tracking performance of the DC bus voltage to a given voltage reference value; the second part is the disturbance current i. o2 The interference with the bus voltage; the third part is the high-frequency loop feedforward term introduced in this design. Based on the previous analysis, it is necessary to design the coefficients of the expression based on the relationship between the actual and observed values ​​of the disturbance current, and to eliminate the disturbance current i. o1 The impact on bus voltage. First, based on the control loop, the expressions for each coefficient can be written:

[0132] (twenty two)

[0133] (twenty three)

[0134] (twenty four)

[0135] The transfer function in the coefficient expression can be obtained through small-signal modeling. By canceling out the second and third parts, the expression for the high-frequency loop feedforward function can be obtained as follows:

[0136] (25)

[0137] At this point, the disturbance current i dc Includes i o1 and i o2 Both disturbance components were completely eliminated, theoretically resolving the DC bus voltage u issue. dc Disturbance factors.

[0138] The optimized control loop incorporating frequency-division feedforward was simulated and verified, using actual collected power data from the plowing and driving of an electric tractor as experimental data. The simulation experiment yielded comparisons of the bus voltage smoothing effect before and after adding frequency-division feedforward control. Figure 5 As shown, the red curve represents the bus voltage fluctuation under traditional PI control, while the blue curve represents the bus voltage fluctuation after adding frequency division feedforward optimization. It can be seen that the blue curve, compared to the red curve, shrinks towards the bus voltage reference value (400V). This indicates that the addition of frequency division feedforward effectively reduces the bus voltage oscillation amplitude, enabling the electric tractor to adapt to more complex external operating conditions. Figure 6-9 Four voltage spikes with significant smoothing effects are shown. It can be seen that frequency-division feedforward greatly reduces the amplitude of voltage fluctuations, reducing voltage oscillations by up to 68.1%, which verifies the rationality and effectiveness of the proposed method. In addition, the detailed voltage fluctuation diagram shows that frequency-division feedforward not only suppresses the oscillation amplitude but also shortens the voltage recovery time, indicating that the proposed method effectively improves the response capability and response speed of the hybrid energy storage system.

[0139] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0140] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment includes only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for smoothing bus voltage fluctuations in a hybrid energy storage system based on frequency division feedforward, characterized in that, Includes the following steps: Step S1: Design a nonlinear disturbance observer to read disturbance information based on state variables such as bus voltage, and then obtain the disturbance components of the corresponding lithium battery and supercapacitor through a frequency division circuit to provide input for feedforward control; Step S2: Design a feedforward function suitable for lithium battery and supercapacitor loops. Inject the frequency-divided disturbance information into the corresponding control loop through the feedforward link, and use the disturbance observation value to eliminate system disturbance and stabilize the bus voltage.

2. The method for smoothing bus voltage fluctuations in a hybrid energy storage system based on frequency division feedforward according to claim 1, characterized in that, The specific process of reading system disturbance information in step S1 includes: Step S1.1: Analyze the sources of disturbance in the system and determine the objects to be observed; Step S1.2: Design a nonlinear disturbance observer to read the disturbance information.

3. The method for smoothing bus voltage fluctuations in a hybrid energy storage system based on frequency division feedforward according to claim 1, characterized in that, Specifically, step S1.1 involves determining the source of disturbance as the bus current: the sudden change in the load torque of the electric tractor causes a surge in the stator current, which in turn causes a sudden increase in the bus current, leading to oscillations in the bus voltage. Therefore, the bus current is taken as the source of system disturbance.

4. The method for smoothing bus voltage fluctuations in a hybrid energy storage system based on frequency division feedforward according to claim 2, characterized in that, Step S1.2 specifically involves: constructing a nonlinear disturbance observer: establishing system equations including bus voltage, inductor current, duty cycle, and bus current based on the system topology; constructing the observer equations and introducing intermediate variables; designing the observation function and gain matrix to make the observer converge, thereby obtaining the disturbance observation value of the bus current. .

5. The method for smoothing bus voltage fluctuations in a hybrid energy storage system based on frequency division feedforward according to claim 4, characterized in that, The system equations are derived from the system structure topology, specifically: (1) (2) (3) (4) Where d1 represents the duty cycle of S1 and S2, and d2 represents the duty cycle of S3 and S4; according to the nonlinear disturbance observer equation, the system equation is assumed to be: (5) Where X is a state variable. This includes bus voltage and inductor current; u is the control input, i.e., the duty cycle. d represents the disturbance, i.e., the bus current. y represents the output, i.e., the bus voltage. f(X) represents the natural state of the system, i.e., without control input or disturbance. ;g u (X) is the control input matrix. ;g d (X) is the perturbation input matrix. ; Next, construct the observer equations: (6) To eliminate Direct dependency, introducing intermediate variables The observer equation is rewritten as: (7) in, Let p(X) be the disturbance observation value; p(X) be the observation function to be designed; and L(X) be the interference gain matrix, which must satisfy: (8) (9) Among them, l i Indicates the feedback gain of the observer; Define the perturbation estimation error e d (t), then we have the disturbance error equation: (10) (11) when The observer will be convergent, with a time constant. At this point, the interference observer equation for the lithium battery loop is: (12) The observed and actual values ​​of the disturbance current have the following relationship: (13) At this point, the object being observed is the DC bus current, i.e., apparent i dc i is the source of system disturbance. dc Includes lithium battery branch i o1 and supercapacitor branch i o2 This indicates that the disturbance source can be divided into two; therefore, when i is obtained dc After dividing the observed values, we obtain feedforward perturbation observations suitable for lithium batteries and supercapacitors; (14) (15) in, This is the cutoff frequency.

6. The method for smoothing bus voltage fluctuations in a hybrid energy storage system based on frequency division feedforward according to claim 1, characterized in that, The specific steps of the frequency division injection feedforward control described in step S2 are as follows: Step S2.1: Inject feedforward control into the low-frequency loop; Step S2.2: Inject feedforward control into the high-frequency loop.

7. The method for smoothing bus voltage fluctuations in a hybrid energy storage system based on frequency division feedforward according to claim 6, characterized in that, The specific steps of S2.1 are as follows: First, the system expression is written based on the PI control loop of the lithium battery branch: (16) The first part of the formula reflects the tracking performance of the DC bus voltage to a given voltage reference value; the second part is the disturbance current i. o1 Interference with bus voltage; The third part is the low-frequency loop feedforward term introduced in this design; Based on the relationship between the actual and observed values ​​of the disturbance current, the coefficients of the expression are designed to eliminate the disturbance current i. o1 Impact on bus voltage; First, based on the control loop, the expressions for each coefficient can be written: (17) (18) (19) By canceling out the second and third parts, we can obtain the expression for the low-frequency loop feedforward function: (20) This theoretically solves the problem of i. o1 For u dc The impact.

8. The method for smoothing bus voltage fluctuations in a hybrid energy storage system based on frequency division feedforward according to claim 6, characterized in that, Step S2.2 specifically involves: First, the system expression is written based on the PI control loop of the lithium battery branch: (21) The first part of the formula reflects the tracking performance of the DC bus voltage to a given voltage reference value; the second part is the disturbance current i. o2 Interference with bus voltage; Part Three is the high-frequency loop feedforward term introduced in this design; Based on the relationship between the actual and observed values ​​of the disturbance current, the coefficients of the expression are designed to eliminate the disturbance current i. o1 The impact on bus voltage; firstly, based on the control loop, the expressions for each coefficient can be written: (22) (23) (24) By canceling out the second and third parts, we can obtain the expression for the high-frequency loop feedforward function: (25) At this point, the disturbance current i dc Includes i o1 and i o2 Both disturbance components were completely eliminated, theoretically resolving the DC bus voltage u issue. dc Disturbance factors.

Images