Networking type energy storage converter nonlinear modeling method based on mixed potential function

Abstract

The invention belongs to the technical field of energy storage and grid connection, and particularly relates to a non-linear modeling method for a network-building type energy storage converter based on a mixed potential function, which comprises the following steps of: in an analysis model of the mixed potential function, determining a group of complete mixed variables of branch current and voltage by a non-energy-storage element and a capacitor; the method comprises the following steps: calculating a product of a current potential function of a non-energy-storage element and a voltage and a current on a capacitor according to an energy relation of system elements according to an inductive current and a capacitor voltage in an energy storage grid-connected system, and further deriving a mixed potential function of the system; and constructing a nonlinear model of the energy storage grid-connected system according to the determined hybrid potential function of the energy storage system. According to the method, the transient stability behavior of a nonlinear circuit is considered from the perspective of energy, the Lyapunov function construction difficulty of a high-order nonlinear system is reduced, and the problem that the transient stability analysis difficulty of the nonlinear system is large under the condition that the system is subjected to large disturbance can be solved.

Description

Technical Field

[0001] The invention belongs to the technical field of energy storage grid connection, and in particular relates to a nonlinear modeling method of a grid-connected energy storage converter based on a mixed potential function. Background Art

[0002] In order to solve the problems caused by the large-scale access of renewable energy to the safe and reliable operation of the power system, large-capacity energy storage technology has received increasing attention from countries around the world. As an important component to solve the high-proportion application of renewable energy, the energy storage system is developing rapidly. With the development of energy storage grid-connected technology, the scale of energy storage grid-connected systems is getting larger and larger, and the responsibility it bears for the safe and stable operation of the power system is also increasing. Its stability is directly related to the corresponding power supply load and the reliable and stable operation of the power system.

[0003] At present, the research on energy storage systems is still in the initial exploration stage. In power grids with weak system strength and low physical inertia, grid-controlled energy storage converters are more suitable. The grid-type energy storage converter adopts a power synchronization strategy similar to that of a synchronous generator. It can achieve synchronization without the help of a phase-locked loop, and can improve the voltage and frequency support capabilities of the converter and enhance the stability of the power system. When supplemented with energy storage elements or reserved spare capacity, the grid-type converter can also provide virtual inertia and damping for the system. However, for the transient large signal transient problem of the grid-type energy storage system, the research objects of the existing grid-type energy storage grid-connected system are mostly focused on the inverter modeling and control of the ideal DC voltage source, which ignores the potential impact of DC voltage dynamics on the system. In addition, compared with the stability of small disturbances, the large signal transient stability of the grid-type energy storage converter presents a more complex form, and the energy storage grid-connected system shows increasingly strong nonlinear characteristics.

[0004] At present, a large number of studies have pointed out that the stability of the grid-connected energy storage system directly affects the stable operation of the entire new energy grid-connected system. The equivalent model of the grid-connected energy storage converter based on small signal disturbance has received widespread attention and achieved remarkable results. However, there is still a lack of equivalent analysis models that can accurately describe the large signal transient behavior of the grid-connected energy storage converter.

[0005] In view of this, the inventor hopes to provide a nonlinear modeling method for a network-type energy storage converter based on a mixed potential function, which can accurately describe the nonlinear characteristics of the system and facilitate the use of a function method to solve the system's Lyapunov function, which is of great significance for the large-signal transient stability analysis of the network-type energy storage converter. Summary of the invention

[0006] The purpose of the present invention is to overcome the above-mentioned problems existing in the traditional technology and to provide a nonlinear modeling method of a grid-type energy storage converter based on a mixed potential function.

[0007] In order to achieve the above technical objectives and the above technical effects, the present invention is implemented through the following technical solutions:

[0008] The present invention provides a nonlinear modeling method for a network-type energy storage converter based on a mixed potential function, comprising the following steps:

[0009] S1. In the analytical model of the mixed potential function, a complete set of mixed variables of branch current and voltage is determined by non-energy storage elements and capacitors;

[0010] S2. According to the inductor current and capacitor voltage in the energy storage grid-connected system, the current potential function of the non-energy storage component and the voltage-current product on the capacitor are calculated from the energy relationship of the system components, and then the mixed potential function of the system is derived;

[0011] S3. constructing a nonlinear model of the energy storage grid-connected system according to the determined mixed potential function;

[0012] Furthermore, in step S1, the inductor current i in the analytical model of the mixed potential function gd 、i d and capacitor voltage V d 、V dc Determined as a complete set of mixed variables in the circuit.

[0013] Furthermore, in step S2, the current potential function of the non-energy storage element is calculated by the inductor current variable in the energy storage grid-connected system:

[0014]

[0015] Among them, i λ 、u λ are the current and voltage on the λth non-energy storage element, r and s indicate that there are r inductor branches and s capacitor branches in the circuit, i and u represent the vectors composed of the current and voltage on the non-energy storage elements and capacitor branches in the circuit, Γ represents the integration area, which refers to the minimum value of the integrated variable to the steady-state value, which is determined by the voltage and current in the system.

[0016] Further, in step S2, the voltage-current product on the capacitor is calculated according to the capacitor voltage variable in the energy storage grid-connected system:

[0017]

[0018] Among them, i σ 、u σ are the current and voltage on the σth capacitor.

[0019] Further, in step S2, the hybrid potential function of the grid-connected energy storage system is calculated based on the current potential function of the non-energy storage element and the voltage-current product on the capacitor:

[0020]

[0021] Among them, -A(i) is the current potential function, B(u) is the voltage potential function, γ is a constant matrix, α is a constant vector, and both γ and α are determined by the circuit topology.

[0022] Furthermore, in step S3, according to the mixed potential function determined in the analytical model of the mixed potential function of the energy storage grid-connected system, the nonlinear model of the system is obtained as follows:

[0023]

[0024] Among them, V gd 、i gd is the grid-connected voltage and current of the inverter, V d 、i d is the voltage and current at the common coupling point, R is the inverter filter resistor, V dc is the DC side voltage of the inverter, P b is the output power of the energy storage unit, d d It is the duty cycle output by the inverter control unit.

[0025] The beneficial effects of the present invention are:

[0026] The present invention provides a nonlinear modeling method for a grid-type energy storage converter based on a hybrid potential function. The method is scientifically and reasonably designed and provides a new idea for the stability analysis of the grid-type energy storage converter. In the stability analysis of the grid-type energy storage converter, it is difficult to select the Lyapunov function according to the traditional energy storage grid-connected system model. In this regard, the large signal model of the grid-type energy storage converter system proposed by the present invention can easily find the Lyapunov function by using the hybrid potential function of the nonlinear circuit model. Compared with the traditional technology, the difficulty of large signal stability analysis of the grid-type energy storage converter is greatly reduced, and it is worthy of being promoted and used.

[0027] Of course, any product implementing the present invention does not necessarily need to achieve all of the above advantages at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for describing the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0029] Figure 1 This is a main circuit diagram of the energy storage grid-connected system in an embodiment of the present invention;

[0030] Figure 2 A typical converter topology diagram in an embodiment of the present invention;

[0031] Figure 3 Schematic diagram of the average model of the converter in the embodiment of the present invention;

[0032] Figure 4 This is a DC side control block diagram of the energy storage grid-connected system in an embodiment of the present invention;

[0033] Figure 5 A hybrid potential function analysis model diagram of an energy storage grid-connected system in an embodiment of the present invention;

[0034] Figure 6 It is a stable waveform diagram of the energy storage grid-connected system in an embodiment of the present invention;

[0035] Figure 7 A comparison diagram of dynamic responses of the energy storage grid-connected system at different power levels in an embodiment of the present invention;

[0036] Figure 8 It is a comparison diagram of voltage variable response of energy storage grid-connected system in an embodiment of the present invention. DETAILED DESCRIPTION

[0037] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] The specific embodiments of the present invention are as follows:

[0039] Example

[0040] Considering the potential impact of the dynamic response of the DC side voltage of the grid-type energy storage converter on the system, the grid-type energy storage adopts a two-stage energy storage system. The main circuit of the grid-type energy storage system consists of Figure 1 express. Figure 2 A typical energy storage converter topology is given, where v a 、v b 、v c is the three-phase grid voltage, v dc is the DC side voltage, L1 is the AC side filter inductor, L g is the grid inductance. The energy storage converter is modeled and the general mathematical model of the energy storage converter is established using the switch function description.

[0041]

[0042] The general mathematical model of the energy storage converter described by the switching function is established in the three-phase stationary coordinate system. Figure 3 As shown. The spatial model component form can be obtained from the converter average model in the three-phase stationary coordinate system. The mathematical models obtained above are all based on the three-phase stationary coordinate system. The AC side is a time-varying AC quantity, and the mutual coupling of parameters is very complex. In order to facilitate analysis, it is necessary to transform the model in the three-phase stationary coordinate system into a model in the two-phase dq coordinate system rotating at the fundamental frequency of the power grid through coordinate transformation, so that the three-phase balanced alternating current quantity becomes a DC quantity. The DC steady-state operating point can be easily obtained to facilitate the linearization of this nonlinear system, which is helpful for the design of the controller.

[0043] From the above, we can get the mathematical model of the converter dq rotating coordinate system. Since the energy storage unit realizes closed-loop control, Figure 4 As shown, the energy storage unit provides power, which is equivalent to a controlled current source according to its current closed-loop control characteristics. Combined with the mathematical model of the inverter dq rotating coordinate system, the hybrid potential function analysis model of the grid-connected energy storage system is obtained as follows: Figure 5 shown.

[0044] In the hybrid potential function analysis model of the grid-connected energy storage system, the inductor current i gd 、i d and capacitor voltage V d 、V dc Determined as a complete set of mixed variables in the circuit.

[0045] The current potential function of the non-energy storage element branch is calculated by the inductor current variable in the grid-connected energy storage system:

[0046] Voltage source V gd The current potential function is:

[0047]

[0048] The current potential function of the filter resistor R is:

[0049]

[0050] Controlled voltage source d d V dc The current potential function is:

[0051]

[0052] Controlled current source d d i d The current potential function is:

[0053]

[0054] Equivalent controlled current source P b / V dc The current potential function is:

[0055]

[0056] The product of the current and voltage of all capacitor branches is calculated based on the capacitor voltage variables in the grid-connected energy storage system:

[0057] Capacitor C f The energy on is:

[0058]

[0059] Capacitor C dc The energy on is:

[0060]

[0061] The mixed potential function of the grid-connected energy storage system is calculated based on the current potential function of the non-energy storage element and the voltage-current product on the capacitor:

[0062]

[0063] Among them, -A(i) is the current potential function, B(u) is the voltage potential function, γ is a constant matrix, α is a constant vector, and both γ and α are determined by the circuit topology.

[0064] Through equations (1) to (7), the nonlinear model of the system can be obtained based on the mixed potential function determined in the analytical model of the mixed potential function of the energy storage grid-connected system:

[0065]

[0066] Among them, P is the nonlinear model of the system, V gd 、i gd is the grid-connected voltage and current of the inverter, V d 、i d is the voltage and current at the common coupling point, R is the inverter filter resistor, V dc is the DC side voltage of the inverter, P b is the output power of the energy storage unit, d d It is the duty cycle output by the inverter control unit.

[0067] Through formula (9), Matlab / Simulink can be used to build an equivalent mathematical model of the hybrid potential function of the grid-connected energy storage system. Figure 6 The equivalent mathematical model of the mixed potential function is used in the embodiment of the present invention to realize the three-phase voltage and three-phase current on the AC side of the grid-connected system operating at a static operating point.

[0068] In this embodiment, in order to verify the effectiveness of the proposed method, the dynamic characteristics of the grid-connected energy storage system are verified, and simulation verification is performed for different system power instructions and system variables in the Matlab / Simulink simulation of the traditional grid-connected energy storage system and the Matlab / Simulink simulation of the equivalent mathematical model of the hybrid potential function. Figure 7 This is the system power simulation waveform when the system power instruction jumps from 10KW to 20KW; Figure 8 The system variable V is when the system power command is 10KW d It can be seen from the simulation waveform that the large signal model of the network-type energy storage system is consistent with the dynamic characteristics of the traditional model, that is, the large signal model of the network-type energy storage converter based on the mixed potential function proposed in this embodiment is correct.

[0069] The above-mentioned embodiment provides a nonlinear modeling method for a grid-type energy storage converter based on a mixed potential function, which provides a new idea for the stability analysis of a grid-type energy storage system. In the stability analysis of a grid-type energy storage converter, it is difficult to select a Lyapunov function based on a traditional grid-type energy storage system model. However, the large signal model of the grid-type energy storage system proposed in this embodiment can easily find the Lyapunov function using the nonlinear circuit equivalent model of the grid-type energy storage converter. Compared with traditional technologies, it greatly reduces the difficulty of large signal stability analysis of a grid-type energy storage system and is worthy of promotion and use.

[0070] The preferred embodiments of the present invention disclosed above are only used to help explain the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to specific implementation methods. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A nonlinear modeling method for a grid-type energy storage converter based on a mixed potential function, characterized in that: The steps include: S1. In the analytical model of the mixed potential function, a complete set of mixed variables of branch current and voltage is determined by non-energy storage elements and capacitors; S2. According to the inductor current and capacitor voltage in the energy storage grid-connected system, the current potential function of the non-energy storage component and the voltage-current product on the capacitor are calculated from the energy relationship of the system components, and then the mixed potential function of the system is derived; S3. Based on the determined mixed potential function, a nonlinear model of the energy storage grid-connected system is constructed.

2. The nonlinear modeling method of a network-type energy storage converter based on a mixed potential function according to claim 1, characterized in that: In step S1, the inductor current i in the analytical model of the mixed potential function gd 、i d and capacitor voltage V d 、V dc Determined as a complete set of mixed variables in the circuit.

3. The nonlinear modeling method of a network-type energy storage converter based on a mixed potential function according to claim 2, characterized in that: In step S2, the current potential function of the non-energy storage element is calculated by the inductor current variable in the energy storage grid-connected system: Among them, i λ 、u λ are the current and voltage on the λth non-energy storage element, r and s indicate that there are r inductor branches and s capacitor branches in the circuit, i and u represent the vectors composed of the current and voltage on the non-energy storage elements and capacitor branches in the circuit, Γ represents the integration area, which refers to the minimum value of the integrated variable to the steady-state value, which is determined by the voltage and current in the system.

4. The nonlinear modeling method of a network-type energy storage converter based on a mixed potential function according to claim 3 is characterized in that: In step S2, the voltage-current product on the capacitor is calculated according to the capacitor voltage variable in the energy storage grid-connected system: Among them, i σ 、u σ are the current and voltage on the σth capacitor.

5. The nonlinear modeling method of a network-type energy storage converter based on a mixed potential function according to claim 4 is characterized in that: In step S2, the mixed potential function of the grid-connected energy storage system is calculated based on the current potential function of the non-energy storage element and the voltage-current product on the capacitor: Among them, -A(i) is the current potential function, B(u) is the voltage potential function, γ is a constant matrix, α is a constant vector, and both γ and α are determined by the circuit topology.

6. The nonlinear modeling method of a network-type energy storage converter based on a mixed potential function according to claim 5 is characterized in that: In step S3, according to the mixed potential function determined in the analytical model of the mixed potential function of the energy storage grid-connected system, the nonlinear model of the system is obtained as follows: Among them, V gd 、i gd is the grid-connected voltage and current of the inverter, V d 、i d is the voltage and current at the common coupling point, R is the inverter filter resistor, V dc is the DC side voltage of the inverter, P b is the output power of the energy storage unit, d d It is the duty cycle output by the inverter control unit.

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