An energy storage inverter control method and system based on interval observer

Abstract

The present application relates to the technical field of energy storage inverter control, and particularly relates to an energy storage inverter control method and system based on an interval observer, which estimates inductance current information by designing an unknown input observer, reduces the dependence of the system on a current sensor, and thus reduces the hardware cost of the system. In addition, the present application also reconstructs unknown load current information by designing an interval observer, and implements feedforward compensation in the controller, thereby improving the output voltage quality of the system under nonlinear load working conditions. The estimated load current can monitor the system in real time and provide overload protection function, thereby reducing the cost of the system and improving the safety and reliability of the system.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of energy storage inverter control, and particularly relates to an energy storage inverter control method and system based on an interval observer. BACKGROUND

[0002] With the transformation of global energy structure and the widespread application of renewable energy, energy storage technology plays an increasingly important role in modern power systems. Energy storage systems effectively regulate the balance between supply and demand of electric energy, optimizing the distribution of power resources, especially in areas with large differences in peak and valley electricity prices, playing an important economic value. Energy storage inverters, as the core equipment connecting energy storage systems and power grids or loads, directly affect the stability and efficiency of the system. However, inverters face complex control challenges when dealing with different load conditions, especially nonlinear loads. These loads can generate significant harmonic currents and dynamic disturbances, leading to a decline in output voltage quality and degradation of system control performance. Therefore, designing a high-performance control method that can cope with nonlinear load disturbances is of great significance to improve the stability and reliability of energy storage systems.

[0003] Since the compensation effect of load current usually directly affects the control performance of the system, existing solutions usually need to collect inductance current to indirectly obtain load current information to design a controller, resulting in increased system cost and reduced reliability. In addition, current research only designs controllers for linear loads without considering uncertain load dynamics, limiting the application scenarios of the system. Therefore, there is an urgent need to provide an energy storage inverter control method that can reduce system cost and improve system safety and reliability. SUMMARY

[0004] The present application provides an energy storage inverter control method and system based on an interval observer to solve the problem of high cost, lack of safety and reliability of the control system in the prior art.

[0005] To achieve the above-mentioned purpose, the present application realizes through the following technical solutions:

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

[0007] S1: establishing an average model of the energy storage inverter, converting the average model into a state space equation, and performing coordinate transformation on the state space equation based on a pre-designed coordinate transformation relationship;

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

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

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

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

[0012] In a second aspect, the present application provides an interval observer-based energy storage inverter control system, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, and the processor implements the steps of the method of the first aspect when executing the computer program.

[0013] Advantages:

[0014] The interval observer-based energy storage inverter control method provided by the present application pre-designs the control, then estimates the output current information used in the control law designed in the step by designing an observer, and obtains a final interval observer-based energy storage inverter control method designed. In this way, the inductance current information is estimated by designing an unknown input observer, the dependence of the system on the current sensor is reduced, and thus the hardware cost of the system is reduced. In addition, the unknown load current information is reconstructed by designing an interval observer, and feedforward compensation is implemented in the controller, and the output voltage quality of the system under the nonlinear load working condition is improved. The estimated load current can monitor the system in real time and provide overload protection function for the system, and the safety and reliability of the system are improved while the cost of the system is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 A flow chart of the interval observer-based energy storage inverter control method of the preferred embodiment of the present application;

[0016] Figure 2 A schematic diagram of the energy storage inverter of the preferred embodiment of the present application;

[0017] Figure 3 A block diagram of the interval observer-based energy storage inverter control method of the embodiment of the present application;

[0018] Figure 4 A schematic diagram of the load system of the energy storage inverter of the embodiment of the present application;

[0019] Figure 5 Simulation results of the interval observer-based energy storage inverter sensorless algorithm of the embodiment of the present application under a linear load;

[0020] Figure 6The simulation result of the energy storage inverter few sensor algorithm based on the interval observer of an embodiment of the present application under a nonlinear load. DETAILED DESCRIPTION

[0021] The technical solutions of the present application will be described clearly and completely below. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of the present application.

[0022] Unless otherwise defined, the technical terms or scientific terms used in the present application shall have the meanings commonly understood by those skilled in the art. The terms "first", "second", and similar terms used in the present application do not represent any order, number, or importance, but are only used to distinguish different components. Similarly, the terms "one" or "a" and similar terms do not represent a quantity limitation, but represent the existence of at least one. The terms "connected" or "connected" and similar terms are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. The terms "up", "down", "left", "right", and the like are only used to represent relative positional relationships, and when the absolute positions of the described objects change, the relative positional relationships also change accordingly.

[0023] Please refer to Figure 1 The present application provides an energy storage inverter control method based on an interval observer, comprising:

[0024] S1: establishing an average model of the energy storage inverter, converting the average model into a state space equation, and performing coordinate transformation on the state space equation based on a pre-designed coordinate transformation relationship;

[0025] S2: determining a pre-designed control law of the control system according to the equation after coordinate transformation combined with the separation principle;

[0026] S3: designing an interval observer, and obtaining a correlation between unknown load current information and states based on the interval observer;

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

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

[0029] The energy storage inverter control method based on the interval observer is pre-designed, then an observer is designed to estimate the output current information used in the control law designed in the step, and finally the energy storage inverter control method based on the interval observer is designed, in this way, the inductor current information is estimated by designing the unknown input observer, the dependence of the system on the current sensor is reduced, and thus the hardware cost of the system is reduced. In addition, the unknown load current information is reconstructed by designing the interval observer, and the feedforward compensation is implemented in the controller, and the output voltage quality of the system under the nonlinear load working condition is improved. The estimated load current can monitor the system in real time and provide overload protection function, which reduces the cost of the system and improves the safety and reliability of the system.

[0030] Next, the steps of the above method are described in detail in a complete embodiment.

[0031] As Figure 2 The energy storage inverter schematic diagram is shown, which includes three parts, that is, a full-bridge inverter part, an LC filter part and a load system part. The control structure diagram of the energy storage inverter control method based on the interval observer is shown in Figure 3 The inductor current and load current information are estimated by combining the interval observer and the unknown input observer. The load voltage information collected by the voltage sensor is combined to form the input of the controller.

[0032] As Figure 4 The load system schematic diagram of the energy storage inverter is shown. The linear load is simulated by resistance, resistance-capacitance load and resistance-inductance load, and the nonlinear load is simulated by uncontrolled rectification circuit plus LC filter and resistance.

[0033] As Figure 5 The simulation result of the energy storage inverter sensorless algorithm based on the interval observer under the linear load is shown. It can be seen from the simulation result that when the linear load system steps, the output voltage does not distort and the dynamic response is fast.

[0034] As Figure 6 The simulation result of the energy storage inverter sensorless algorithm based on the interval observer under the nonlinear load is shown. It can be seen from the simulation result that under the nonlinear load working condition, the output voltage does not distort and does not have high-order harmonics. When the nonlinear load system steps, the output voltage does not distort and the dynamic response is fast.

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

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

[0037]

[0038] Where L and C represent the filter inductance and filter capacitor of the inverter, respectively, and R L This represents the equivalent resistance of the filter inductor L. o i L and i o These represent the output voltage, inductor current, and output current, respectively. E represents the DC-side voltage, and μ represents the control input. Since only the output voltage is sampled, the system only has v. o It is feedback-enabled, i o and i L All of these require the design of an observer for estimation.

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

[0040]

[0041] in Represents state variables, Represents the system matrix. Represents the input matrix, Indicates the output matrix. Perturbation input matrix and The disturbance to be estimated, d v This indicates the disturbance to be estimated.

[0042] To eliminate the adverse effects of the mismatched disturbance d on the system, a coordinate transformation is designed:

[0043]

[0044] In the formula, x1 and x2 represent the state variables obtained after coordinate transformation. The equivalent form that can be obtained based on the coordinate transformation relationship is:

[0045]

[0046] in This represents the new state variable after the coordinate transformation. Represents the new system matrix. Let C represent the new input matrix. x =[1 0] represents the new output matrix, and Let d represent the derivative of d. It can be observed that after coordinate transformation, the unmatched perturbation d has been transformed into a matched perturbation.

[0047] In 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] The intermediate y m represents the reference of output voltage, represents the derivative of the reference of output voltage.

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

[0052]

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

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

[0055]

[0056] Wherein represents the control law gain vector. In order to ensure the stability of the tracking error system, the appropriate is selected to ensure that the matrix is a Hurwitz matrix. represents the second derivative of the reference of output voltage, represents the estimated system error, represents the estimated value of , represents the estimated value of inductance current i L .

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

[0058] The interval observer is designed as follows for the original system:

[0059]

[0060] Wherein and z represent the upper bound and lower bound of the state z, and the initial value z(0) is unknown but bounded, satisfying and the upper and lower bounds z (0) and of z are known. and d represent the upper bound and lower bound of the unknown disturbance, satisfying Mz is the gain vector of the interval observer. To ensure that the designed interval observer always satisfies the designed interval observer gain vector M z It is required to guarantee that the matrix A z - M z C z is not only Hurwitz matrix, but also Metzler matrix. denotes the maximum value of the matrix D z compared to 0, denotes the maximum value of the matrix -D z compared to 0.

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

[0062]

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

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

[0065]

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

[0067]

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

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

[0070]

[0071] Taking the derivative along the trajectory of can be obtained:

[0072]

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

[0074]

[0075] Taking the derivative of y along the trajectory of t with respect to time, we have:

[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 y along the trajectory of t with respect to time, we have:

[0080]

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

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

[0083]

[0084] By 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 , and 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, an unknown input observer is designed to obtain the estimated value of the inductor current and the load current. Combined with the controller designed in step S2, the final designed control law is obtained, and the specific process is as follows:

[0088] Based on the design of the unknown input observer:

[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 be guaranteed is a Hurwitz matrix. The time-varying function is solved by the formula.

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

[0092]

[0093] The embodiment of the present application also provides an energy storage inverter control system based on an interval observer, which comprises a memory, a processor and a computer program stored in the memory and executable on the processor, and the processor implements the steps of the above method when executing the computer program. The energy storage inverter control system based on the interval observer can implement each embodiment of the above method and achieve the same beneficial effects, and thus will not be described here in detail.

[0094] The preferred embodiments of the present application are described in detail above. It should be understood that those skilled in the art can make many modifications and variations without creative work based on the concept of the present application. Therefore, any technical solution obtained by logical analysis, reasoning or limited experiment based on the existing technology according to the concept of the present application shall be within the protection scope defined by the claims.

Claims

1. An interval observer based energy storage inverter control method, characterized by, The method comprises the following steps: S1: establishing an average model of the energy storage inverter, converting the average model into a state space equation, and performing coordinate transformation on the state space equation based on a pre-designed coordinate transformation relationship; S2: determining a pre-designed control law of the control system according to the equation after coordinate transformation and the separation principle; S3: designing an interval observer, and obtaining a correlation between unknown load current information and states based on the interval observer; S4: designing an unknown input observer according to the correlation; S5: obtaining estimated values of inductor current and load current based on the unknown input observer, and obtaining a final energy storage inverter control method based on the interval observer based on the pre-designed control law.

2. The interval observer based energy storage inverter control method of claim 1, wherein, The S1 comprises: According to Kirchhoff's law, the average model of the inverter is expressed as follows: where L and C represent the filter inductance and filter capacitance of the inverter, respectively, R L represents the equivalent resistance of the filter inductance L, v o , i L , and i o represent the output voltage, inductance current, and output current, respectively, E represents the DC-side voltage, and μ represents the control input; The output voltage v is defined as o The inductor current i is the state variable z1 L The state variable z2 will be written in the form of a state space equation as follows: where z represents a state variable, A Z represents a system matrix, B Z represents an input matrix, C Z represents an output matrix, D Z represents a disturbance input matrix, d v represents a disturbance to be estimated; A coordinate transformation is designed to satisfy the following relationship: In the formula, x1 and x2 represent state variables obtained after coordinate transformation; and an equivalent form obtained based on the relationship of the coordinate transformation is as follows: where x denotes the new state variable after the coordinate transformation, A x denotes the new system matrix, B x denotes the new input matrix, C x denotes the new output matrix, denotes the derivative of the disturbance d v to be estimated.

3. The interval observer based energy storage inverter control method of claim 2, wherein, The S2 comprises: The reference vector of the equation after coordinate transformation satisfies the following relationship: In the meantime, y m represents a reference for the output voltage, represents a derivative of the output voltage reference; The tracking error vector e = y is defined as mv - x, and the dynamic equation of the tracking error system is constructed as follows: where e1 represents the tracking error of the output voltage, e1 = y m -y, denotes the derivative of the output voltage reference vector; A pre-designed control law of the system is constructed according to the dynamic equation of the tracking error system and the separation principle, and satisfies the following relationship: where μ denotes the control input, denotes the control law gain vector, denotes the second derivative of the output voltage reference, denotes the estimated system error, R L denotes the equivalent resistance of the filter inductance L, denotes the estimated value of the derivative of the disturbance d v to be estimated, L and C denote the filter inductance and filter capacitance of the inverter, respectively, and E denotes the DC-side voltage, denotes the estimated value of the inductor current i L .

4. The interval observer based energy storage inverter control method of claim 3, wherein, The interval observer in the S3 satisfies the following relationship: wherein and z denotes the upper and lower bounds of the state variable z, and d v denote the upper and lower bounds of the unknown disturbance, M z is the gain vector of the interval observer, denotes the maximum value compared to the matrix D z and 0, denotes the maximum value compared to the matrix -D z and 0.

5. The interval observer based energy storage inverter control method of claim 4, wherein, The S3 comprises: An interval observer is designed, defining an interval error vector The dynamic equation of the interval error vector is obtained from the interval observer: wherein denotes an intermediate computational variable, in particular a perturbation d v the upper bound minus the lower bound of the expression The interval estimation of the system output y is described as follows: wherein and y denote the upper and lower bounds of the output y, respectively, then: wherein denotes an intermediate computational variable, in particular the upper bound of the output y minus the lower bound, expressed as: It is assumed that a time-varying function α(t) of the system satisfies the following relationship: The derivative of along the trajectory is obtained as follows: wherein is an intermediate calculation variable, the specific expression of which is: The derivative of y with respect to time along the trajectory is obtained as follows: where f2(x, y) is an intermediate calculation variable, with the specific expression: x f2(x, y) = (x - y)2 The derivative of with respect to time along the trajectories of and is obtained as follows: wherein denotes the derivative of the time-varying function a; Similarly, the state space equation is obtained as follows: Simultaneously and obtain unknown disturbance d v The relationship between the state z and the unknown load current information satisfies the following relationship: wherein denotes the matrix C z D z the pseudo inverse of 6. The interval observer based energy storage inverter control method of claim 5, wherein, The unknown input observer in the S4 satisfies the following relationship: wherein denotes the derivative of the vector z estimate, denotes the estimate of the variable z, denotes the estimate of the unknown disturbance d v , K o denotes the observer gain vector to be designed, and a denotes a time-varying function.

7. The interval observer based energy storage inverter control method of claim 6, wherein, The final energy storage inverter control method based on the interval observer satisfies the following relationship: where μ represents a control input, L and C represent a filter inductance and a filter capacitance of the inverter, respectively, R L represents an equivalent resistance of the filter inductance L, v o represents an output voltage, E represents a DC-side voltage, represents an estimated value of a derivative of a disturbance d to be estimated, represents an estimated value of an unknown disturbance d, represents a second derivative of an output voltage reference, represents a control law gain vector, represents an estimated system error, represents an estimated value of a variable z2, represents a derivative of an output voltage reference, represents a derivative of a vector z estimated value, A Z represents a system matrix, B Z represents an input matrix, C Z represents an output matrix, D Z a disturbance input matrix, K o represents an observer gain vector to be designed, α represents a time-varying function, represents a derivative of the time-varying function α.

8. A storage inverter control system based on an interval observer, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, The processor implements the steps of the method of any one of claims 1 to 7 when executing the computer program.

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