Energy storage inverter control method and system based on interval observer

Abstract

The invention relates to the technical field of energy storage inverter control, in particular to an energy storage inverter control method and system based on an interval observer, and the method estimates inductive current information through designing an unknown input observer, reduces the dependence of the system on a current sensor, and reduces the hardware cost of the system. Besides, unknown load current information is reconstructed by designing an interval observer, and feed-forward compensation is implemented in the controller, so that the output voltage quality of the system under a nonlinear load working condition is improved. The estimated load current can monitor the system in real time and provide an overload protection function for the system, and the safety and reliability of the system are improved while the cost of the system is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of energy storage inverter control, and particularly to a control method and system for an energy storage inverter based on an interval observer. Background Art

[0002] With the transformation of the global energy structure and the wide application of renewable energy, energy storage technology plays an increasingly important role in modern power systems. Energy storage systems effectively regulate the balance between power supply and demand, optimize the allocation of power resources, and particularly play an important economic value in areas with large differences in peak and valley electricity prices. As the core device connecting the energy storage system with the power grid or load, the performance of the energy storage inverter directly affects the stability and efficiency of the system. However, when dealing with different load conditions, especially non-linear loads, the inverter faces relatively complex control challenges. These loads generate significant harmonic currents and dynamic disturbances, leading to a decline in the quality of the output voltage and deterioration of the system control performance. Therefore, designing a high-performance control method that can cope with non-linear load disturbances is of great significance for improving the stability and reliability of energy storage systems.

[0003] Since the compensation effect of the load current usually directly affects the control performance of the system, existing solutions usually need to indirectly obtain the load current information by collecting the inductor current to design the controller, resulting in increased system cost and decreased reliability. In addition, current research only designs controllers for linear loads and does not consider uncertain load dynamics, resulting in limited application scenarios for the system. Therefore, there is an urgent need to provide a control method for an energy storage inverter that can reduce system costs and improve system safety and reliability. Summary of the Invention

[0004] The present invention provides a control method and system for an energy storage inverter based on an interval observer to solve the problems of high cost, lack of safety and reliability in the existing control system.

[0005] To achieve the above object, the present invention is realized by the following technical solutions:

[0006] In the first aspect, the present invention provides a control method for an energy storage inverter based on an interval observer, including:

[0007] S1: Establish an average model of the energy storage inverter, convert the average model into a state space equation, and perform a coordinate transformation on the state space equation based on a pre-designed coordinate transformation relation;

[0008] S2: Determine the pre-designed control law of the control system according to the equation after coordinate transformation in combination with the separation principle;

[0009] S3: Design an interval observer, and obtain the correlation between the unknown load current information and the state based on the interval observer;

[0010] S4: Design an unknown input observer according to the correlation;

[0011] S5: Obtain the estimated values of the inductor current and the load current based on the unknown input observer, and obtain the final energy storage inverter control method based on the interval observer based on the pre-designed control law.

[0012] In a second aspect, the present application provides an energy storage inverter control system based on an interval observer, including a memory, a processor, and a computer program stored on the memory and executable on the processor. When the processor executes the computer program, the steps of the method described in the first aspect above are implemented.

[0013] Beneficial effects:

[0014] The energy storage inverter control method based on the interval observer provided by the present invention pre-designs the control, and then designs an observer to estimate the output current information used in the control law designed in the previous step, and obtains the finally designed energy storage inverter control method based on the interval observer. In this way, the inductor current information is estimated by designing an unknown input observer, reducing the system's dependence on current sensors, thereby reducing the system hardware cost. In addition, the present invention also reconstructs the unknown load current information by designing an interval observer and implements feedforward compensation in the controller, improving the output voltage quality of the system under non-linear load conditions. The estimated load current can monitor the system in real time and provide an overload protection function for it, improving the safety and reliability of the system while reducing the system cost. Description of the drawings

[0015] Figure 1 It is a flowchart of the energy storage inverter control method based on the interval observer according to the preferred embodiment of the present invention;

[0016] Figure 2 It is a schematic diagram of the energy storage inverter according to the preferred embodiment of the present invention;

[0017] Figure 3 It is a block diagram of the energy storage inverter control method based on the interval observer according to the embodiment of the present invention;

[0018] Figure 4 It is a schematic diagram of the load system of the energy storage inverter according to the embodiment of the present invention;

[0019] Figure 5 It is a simulation result of the energy storage inverter multi-sensor algorithm based on the interval observer under linear load according to the embodiment of the present invention;

[0020] Figure 6Simulation results of the sensorless algorithm for energy storage inverters based on interval observers in the present invention embodiments under nonlinear loads. Detailed implementation manners

[0021] The technical solutions of the present invention will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0022] Unless otherwise defined, the technical terms or scientific terms used in the present invention shall have the ordinary meanings understood by those of ordinary skill in the art to which the present invention belongs. The "first", "second" and similar terms used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. Similarly, the terms such as "a" or "one" do not indicate a quantity limitation, but indicate that there is at least one. The terms such as "connected" or "coupled" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. The terms such as "upper", "lower", "left" and "right" are only used to represent relative positional relationships. When the absolute position of the object being described changes, the relative positional relationship also changes accordingly.

[0023] Please refer to Figure 1 , a control method for an energy storage inverter based on an interval observer provided by the present application, includes:

[0024] S1: Establish an average model of the energy storage inverter, convert the average model into a state space equation, and perform a coordinate transformation on the state space equation based on a pre-designed coordinate transformation relation;

[0025] S2: Determine a pre-designed control law for the control system according to the equation after coordinate transformation in combination with the separation principle;

[0026] S3: Design an interval observer, and obtain the correlation relationship between the unknown load current information and the state based on the interval observer;

[0027] S4: Design an unknown input observer according to the correlation relationship;

[0028] S5: Obtain the estimated values of the inductor current and the load current based on the unknown input observer, and obtain the final control method for the energy storage inverter based on the interval observer based on the pre-designed control law.

[0029] The above-mentioned energy storage inverter control method based on an interval observer pre-designs the control, and then designs an observer to estimate the output current information used in the control law designed in the previous step, resulting in the finally designed energy storage inverter control method based on an interval observer. In this way, the inductor current information is estimated by designing an unknown input observer, reducing the system's dependence on current sensors and thus reducing the system's hardware cost. In addition, the present invention also reconstructs the unknown load current information by designing an interval observer and implements feedforward compensation in the controller, improving the output voltage quality of the system under non-linear load conditions. The estimated load current can monitor the system in real time and provide an overload protection function for it, enhancing the system's safety and reliability while reducing the system cost.

[0030] Next, a complete embodiment is used to describe the steps of the above method in detail.

[0031] As Figure 2 shown in the schematic diagram of the energy storage inverter, it includes three parts, namely the full-bridge inverter part, the LC filter part, and the load system part. Among them, the control structure diagram of the energy storage inverter control method based on an interval observer is as Figure 3 shown. It estimates the inductor current and load current information by combining an interval observer and an unknown input observer. Combining the load voltage information collected by the voltage sensor, they jointly constitute the controller input.

[0032] As Figure 4 shown, the schematic diagram of the load system of the energy storage inverter. Linear loads are simulated by resistors, resistive-capacitive loads, and resistive-inductive loads, while non-linear loads are simulated by an uncontrolled rectifier circuit plus an LC filter and a resistor.

[0033] As Figure 5 shown, the simulation results of the energy storage inverter multi-sensor algorithm based on an interval observer under linear loads. It can be seen from the simulation results that when a step occurs in the linear load system, the output voltage does not distort and the dynamic response is fast.

[0034] As Figure 6 shown, the simulation results of the energy storage inverter multi-sensor algorithm based on an interval observer under non-linear loads. It can be seen from the simulation results that under non-linear load conditions, the output voltage has no distortion and no high-order harmonics. When a step occurs in the non-linear load system, the output voltage does not distort and the dynamic response is fast.

[0035] Specifically, the specific process of coordinate transformation in step S1 is as follows:

[0036] According to Kirchhoff's law, the average model of the inverter can be expressed as:

[0037]

[0038] Among them, L and C respectively represent the filter inductor and filter capacitor of the inverter, and R L represents the equivalent resistance of the filter inductor L. v o , i L and i o respectively represent the output voltage, inductor current, and output current. E represents the DC-side voltage, and μ represents the control input. Since only the output voltage is collected, only v o is feedbackable in the system, and both i o and i L need to design an observer to estimate.

[0039] Define the output voltage v o as the state variable z1, and the inductor current i L as the state variable z2. It can be written in the form of a state-space equation:

[0040]

[0041] Among them represents the state variable, represents the system matrix, represents the input matrix, represents the output matrix, the disturbance input matrix, and the disturbance to be estimated, d v represents the disturbance to be estimated.

[0042] To eliminate the adverse effects of the unmatched disturbance d on the system, by designing a coordinate transformation:

[0043]

[0044] In the formula, x1 and x2 represent the state variables obtained after the coordinate transformation. Based on the relational formula of the coordinate transformation, the equivalent form can be obtained as:

[0045]

[0046] Among them represents the new state variable after the coordinate transformation, represents the new system matrix, represents the new input matrix, C x = [1 0] represents the new output matrix, and represents the derivative of d. It can be found that after the coordinate transformation, the unmatched disturbance d has been transformed into a matched disturbance

[0047] In the step S2, based on the separation principle, the specific process of pre-designing the system controller is as follows:

[0048] The defined reference vector is:

[0049]

[0050] where y m represents the reference of the output voltage, represents the derivative of the output voltage reference.

[0051] Define the tracking error vector e = y mv -x. Combining and, the dynamic equation of the tracking error system can be obtained as:

[0052]

[0053] where e1 = y m -y represents the tracking error of the output voltage, represents the derivative of the output voltage reference vector.

[0054] According to, combining the separation principle, the pre-designed control law of the system can be obtained as:

[0055]

[0056] where represents the control law gain vector. To ensure the stability of the tracking error system, by selecting an appropriate to ensure that the matrix is a Hurwitz matrix. represents the second derivative of the output voltage reference, represents the estimated system error, represents the estimated value of, represents the estimated value of the inductor current i L of.

[0057] In step S3, by designing an interval observer, the relationship between the unknown load current information and the state is constructed. The specific process is as follows:

[0058] For the original system, design an interval observer as follows:

[0059]

[0060] where and z represent the upper and lower bounds of the state z, and its initial value z(0) is unknown but bounded, satisfying and its upper and lower bounds z (0) and are known. and d represent the upper and lower bounds of the unknown disturbance, satisfying Mz is the gain vector of the interval observer. To ensure that for all t > 0, the designed interval observer always satisfies the designed interval observer gain vector M z needs to ensure that the matrix A z -M z C z is not only a Hurwitz matrix but also a Metzler matrix. denotes taking the maximum value of the matrix D z compared with 0, denotes taking the maximum value of the matrix -D z compared with 0.

[0061] By defining the interval error vector the dynamic equation of the interval error vector can be obtained from

[0062]

[0063] where denotes an intermediate calculation variable, specifically the upper bound of the disturbance d v minus the lower bound, and the specific expression is

[0064] Since C in z ≥ 0, the interval estimate of the system output y can be described as:

[0065]

[0066] where and y denote the upper and lower bounds of the output y, respectively. In addition, it can also be obtained that:

[0067]

[0068] In the formula, denotes an intermediate calculation variable, specifically the upper bound of the output y minus the lower bound, and the specific expression is

[0069] Assume that the system has a time-varying function a(t) that satisfies:

[0070]

[0071] Taking the derivative of

[0072]

[0073] along the trajectory of has no actual physical meaning and is an intermediate calculation variable, and the specific expression is:

[0074]

[0075] Taking the derivative of y with respect to time along the trajectory gives:

[0076]

[0077] where f2( x , y) has no actual physical meaning and is an intermediate calculation variable, and its specific expression is:

[0078]

[0079] Taking the derivative of along the trajectories of and with respect to time gives:

[0080]

[0081] where represents the derivative of the time-varying function α.

[0082] Similarly, from the system to be observed, we have:

[0083]

[0084] Combining and, the relationship between the unknown disturbance d and the state z can be obtained as:

[0085]

[0086] where, represents the pseudo-inverse of the matrix C z D z . Through the designed interval observer, the relationship between the unknown load current and the state is obtained.

[0087] In step S4, according to the relationship between the unknown load current and the state obtained in step S3, by designing an unknown input observer, the estimated values of the inductor current and the load current are obtained. Combining with the controller designed in step S2, the finally designed control law is obtained. The specific process is as follows:

[0088] Based on the design, the unknown input observer is:

[0089]

[0090] where, represents the derivative of the estimated value of the vector z, where represents the estimated value of the variable z, represents the estimated value of the unknown disturbance d. K o represents the observer gain vector to be designed. To ensure the stability of the observer, the designed observer gain vector K o needs to ensure is a Hurwitz matrix. The time-varying function is obtained by solving the formula.

[0091] Combined with the controller designed in step S2, finally, the energy storage inverter control method based on the interval observer proposed by the present invention is as follows:

[0092]

[0093] The embodiment of the present application also provides an energy storage inverter control system based on an interval observer, including a memory, a processor, and a computer program stored on the memory and executable on the processor. When the processor executes the computer program, the steps of the above method are implemented. The energy storage inverter control system based on the interval observer can implement various embodiments of the above method and achieve the same beneficial effects, which will not be elaborated here.

[0094] The preferred specific embodiments of the present invention have been described in detail above. It should be understood that those of ordinary skill in the art can make many modifications and variations based on the concept of the present invention without creative work. Therefore, all technical solutions that can be obtained by those skilled in the art in the technical field of the present invention through logical analysis, reasoning, or limited experiments based on the concept of the present invention on the basis of the prior art should be within the protection scope determined by the claims.

Claims

1. A control method for an energy storage inverter based on an interval observer, characterized in that, Including: S1: Establish an average model of the energy storage inverter, convert the average model into a state-space equation, and perform coordinate transformation on the state-space equation based on a pre-designed coordinate transformation relationship; S2: Determine the pre-designed control law of the control system according to the equation after coordinate transformation in combination with the separation principle; S3: Design an interval observer, and obtain the correlation relationship between the unknown load current information and the state based on the interval observer; S4: Design an unknown input observer according to the correlation relationship; S5: Obtain the estimated values of the inductor current and the load current based on the unknown input observer, and obtain the final energy storage inverter control method based on the interval observer based on the pre-designed control law.

2. The energy storage inverter control method based on an interval observer according to claim 1, wherein The S1 includes: According to Kirchhoff's law, the average model of the inverter is expressed as follows: Among them, L and C respectively represent the filter inductor and filter capacitor of the inverter, and R L represents the equivalent resistance of the filter inductor L, v o 、i L and i o respectively represent the output voltage, inductor current and output current, E represents the DC-side voltage, and μ represents the control input; Define the output voltage v o as the state variable z1, the inductor current i L as the state variable z2, and write it in the form of state space equations as follows: where z represents the state variable, A Z represents the system matrix, B Z represents the input matrix, C Z represents the output matrix, D Z the disturbance input matrix, d v represents the disturbance to be estimated; Design a coordinate transformation to satisfy the following relationship: Wherein, x1 and x2 represent the state variables obtained after coordinate transformation; the equivalent form obtained based on the coordinate transformation relationship is as follows: Among them, x represents the new state variable after coordinate transformation, A x represents the new system matrix, B x represents the new input matrix, C x represents the new output matrix, represents the disturbance d to be estimated v derivative of.

3. The energy storage inverter control method based on an interval observer according to claim 1, characterized in that The S2 includes: The reference vector of the equation after coordinate transformation satisfies the following relationship: Among them, y m represents the reference of the output voltage, represents the derivative of the output voltage reference; Define the tracking error vector \(e = y\) mv - \(x\), and construct the dynamic equation of the tracking error system as follows: where e1 represents the tracking error of the output voltage, e1 = y m - y, represents the derivative of the output voltage reference vector; Construct the pre-designed control law of the system according to the dynamic equation of the tracking error system in combination with the separation principle, which satisfies the following relationship: where, μ represents the control input, represents the control law gain vector, represents the second derivative of the output voltage reference, represents the estimated system error, R L represents the equivalent resistance of the filter inductor L, represents the disturbance d to be estimated v the estimated value of the derivative of, L and C respectively represent the filter inductor and filter capacitor of the inverter, E represents the DC side voltage, represents the estimated value of the inductor current i L of.

4. The energy storage inverter control method based on an interval observer according to claim 1, characterized in that The interval observer in the S3 satisfies the following relationship: In the formula, and z represent the upper and lower bounds of the state variable z, and d v represent the upper and lower bounds of the unknown disturbance, M z is the gain vector of the interval observer, represents taking the maximum value of matrix D z compared with 0, represents taking the maximum value of matrix -D z compared with 0.

5. The energy storage inverter control method based on an interval observer according to claim 4, wherein, The S3 includes: Design an interval observer and define an interval error vector Obtain the dynamic equation of the interval error vector based on the interval observer: Among them, represents an intermediate calculation variable, specifically the perturbation d v the upper bound minus the lower bound, and the expression is: Describe the interval estimation of the system output y as: wherein, and y respectively represent the upper and lower bounds of the output y, then: In the formula, represents an intermediate calculation variable, specifically the upper bound of the output y minus the lower bound, and the expression is: Assume that the system has a time-varying function a(t) that satisfies: Derive along the trajectory of to obtain: Among them, is an intermediate calculation variable, and the specific expression is: Derive y along the trajectory of with respect to time to obtain: where f2( x , y) is an intermediate calculation variable, and the specific expression is: Derive along the trajectories of and with respect to time to obtain: wherein, represents the derivative of the time-varying function α; Similarly, obtain from the state-space equation: Solve the equations simultaneously to obtain the unknown disturbance d v The relationship between and the state z, regarded as the relationship between the unknown load current information and the state, satisfies the following equation: Among them, represents the matrix C z D z pseudo-inverse of 6. The energy storage inverter control method based on an interval observer according to claim 1, wherein The unknown input observer in the S4 satisfies the following relationship: Among them, represents the derivative of the estimated value of vector z, represents the estimated value of variable z, represents the estimated value of the unknown perturbation d v , K o represents the observer gain vector to be designed, and α represents a time-varying function.

7. The energy storage inverter control method based on an interval observer according to claim 1, wherein The final energy storage inverter control method based on the interval observer satisfies the following relationship: where, μ represents the control input, L and C respectively represent the filter inductor and filter capacitor of the inverter, and R L represents the equivalent resistance of the filter inductor L, v o represents the output voltage, E represents the DC-side voltage, represents the estimated value of the derivative of the disturbance d to be estimated, represents the estimated value of the unknown disturbance d, represents the second derivative of the output voltage reference, represents the control law gain vector, represents the estimated system error, represents, represents the derivative of the output voltage reference, represents the derivative of the estimated value of the vector z, A Z represents the system matrix, B Z represents the input matrix, C Z represents the output matrix, D Z disturbance input matrix, K o represents the observer gain vector to be designed, α represents a time-varying function, represents the derivative of the time-varying function α.

8. A control system for an energy storage inverter based on an interval observer, comprising a memory, a processor, and a computer program stored on the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the steps of the method described in any one of the above claims 1 to 7.

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