Harmonic optimization method, system, equipment, medium and product based on frequency doubling circulation injection

Abstract

The invention discloses a harmonic optimization method, system, equipment, medium and product based on double-frequency circulation injection, and the method comprises the steps: injecting an initial double-frequency circulation into a target extensible cascaded H-bridge energy storage system, updating a three-phase current, combining an initial bias voltage, determining a DC side current of the target extensible cascaded H-bridge energy storage system, and carrying out the harmonic optimization of the target extensible cascaded H-bridge energy storage system. Extracting a direct-current component and a fundamental component in the direct-current side current, determining the fundamental content in each phase of direct-current side current of the target extensible cascaded H-bridge energy storage system according to the direct-current component and the fundamental component, and taking the mean value minimization of the fundamental content in each phase of direct-current side current as an optimization target. And by taking the difference limit value of the fundamental wave content of the direct current side of each phase as a constraint condition and utilizing the constructed harmonic optimization model and the solved optimal parameter, the injection of the double-frequency circulating current and the bias voltage can be accurately controlled, so that the performance of the system is improved, and the balance among the direct current side currents of each phase is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of power system optimization, and in particular to a harmonic optimization method, system, equipment, medium and product based on double frequency circulating current injection. Background Art

[0002] From a system architecture perspective, traditional distribution networks are primarily designed for unidirectional power transmission. However, the integration of distributed renewable energy sources has led to the normalization of bidirectional power flow, making it difficult for existing control equipment to effectively cope with this, potentially leading to a decline in power supply quality and voltage stability issues. From an operational perspective, the randomness and volatility of renewable energy sources further complicates system power balancing, particularly when dealing with high-power DC loads such as electric vehicle charging stations and data centers. This puts the carrying capacity of traditional distribution facilities under severe pressure. Furthermore, with urban land shortages and limited power access resources, the contradiction between the expansion and transformation of distribution networks and the integration needs of new loads is becoming increasingly prominent. These technical bottlenecks seriously affect the safe and stable operation of the power system and urgently need to be effectively resolved through technological innovation and equipment upgrades.

[0003] To address the above technical difficulties, there is an expandable cascaded H-bridge energy storage system (exCHB-ESS). The structure adopts a triangular CHB-ESS design. The specific structure is as follows: Figure 1 As shown. Figure 2 As shown, the high-voltage direct-mounted energy storage system has a stacked structure, which consists of multiple independently controlled upper and lower half-bridge units, and realizes cascade expansion of sub-modules through a dual DC bus configuration.

[0004] To reduce battery-side power fluctuations and extend battery life based on the exCHB-ESS topology, it is necessary to effectively suppress the harmonic components in the DC current. Currently, the traditional method of adding series inductors to the power branches makes it difficult to accurately and quickly suppress the harmonic components in the exCHB-ESS DC current, resulting in poor operational reliability of the scalable cascaded H-bridge energy storage system. Summary of the Invention

[0005] In view of this, the present invention provides a harmonic optimization method, system, device, medium, and product based on double-frequency circulating current injection. This solves the technical problem that the traditional method of using series inductors in power branches cannot accurately and quickly suppress the harmonic components in the DC side current of the exCHB-ESS, resulting in poor operational reliability of the scalable cascaded H-bridge energy storage system.

[0006] A first aspect of the present invention provides a harmonic optimization method based on double frequency circulating current injection, comprising:

[0007] Injecting an initial doubled frequency circulating current into a target scalable cascade H-bridge energy storage system, updating the three-phase current of the target scalable cascade H-bridge energy storage system, and determining the DC side current of the target scalable cascade H-bridge energy storage system based on the three-phase current combined with the initial bias voltage;

[0008] Extracting a DC component and a fundamental component from the DC side current, and determining a fundamental content in the DC side current of each phase of the target scalable cascade H-bridge energy storage system based on the DC component and the fundamental component;

[0009] The harmonic optimization model is constructed with the minimization of the mean value of the fundamental wave content in the DC side current of each phase as the optimization goal and the limit of the difference of the fundamental wave content of each phase DC side as the constraint condition.

[0010] Finding an optimal solution for the harmonic optimization model, and determining an optimal double frequency circulating current and an optimal bias voltage according to the optimal solution;

[0011] Harmonic optimization is performed on the target scalable cascade H-bridge energy storage system using the optimal doubled frequency circulating current and the optimal bias voltage.

[0012] Preferably, the injecting of an initial doubled frequency circulating current into the target scalable cascade H-bridge energy storage system, updating the three-phase current of the target scalable cascade H-bridge energy storage system, and determining the DC side current of the target scalable cascade H-bridge energy storage system based on the three-phase current combined with the initial bias voltage includes:

[0013] Injecting an initial doubled frequency circulating current into a delta-connected circuit of the target scalable cascade H-bridge energy storage system to obtain a three-phase current after superimposing the doubled frequency circulating current;

[0014] Determining the bias-modulated AC side output voltage according to the target scalable AC side output voltage of the cascaded H-bridge energy storage system and the initial bias voltage;

[0015] Determining the switching functions of the upper and lower half bridges of each phase and each submodule according to the bias-modulated AC side output voltage and the DC side voltage of the target scalable cascade H-bridge energy storage system;

[0016] The DC side current of the target expandable cascade H-bridge energy storage system is determined according to the switching functions of the upper and lower half bridges of each phase and each submodule and the three-phase current after the doubled frequency circulating current is superimposed.

[0017] Preferably, the values ​​of the switching functions of the upper and lower half bridges of each phase and each submodule are between 0 and 1.

[0018] Preferably, extracting the DC component and the fundamental component in the DC side current, and determining the fundamental content in the DC side current of each phase of the target scalable cascade H-bridge energy storage system according to the DC component and the fundamental component, includes:

[0019] Extracting a DC component and a fundamental component from the DC side current, and determining the DC component amplitude and the fundamental component amplitude respectively;

[0020] The fundamental content in the DC side current of each phase of the target expandable cascade H-bridge energy storage system is determined based on the ratio of the fundamental component amplitude to the DC component amplitude.

[0021] Preferably, the objective function corresponding to the optimization objective is:

[0022] Where, is the mean value of the fundamental wave content in the DC side current of each phase, is the amplitude of the double frequency circulating current, is the double frequency circulation phase angle, is the bias voltage of ab phase, is the bias voltage of phase bc, is the bias voltage of the ca phase, 、 are the fundamental frequency contents of the upper and lower half-bridge DC sides of the ab phases, 、 are the fundamental frequency contents of the upper and lower half-bridge DC sides of phase bc, respectively. 、 are the fundamental frequency contents of the upper and lower half-bridge DC sides of phase ca, respectively;

[0023] The constraints are:

[0024]

[0025] Where, 、 are the switching functions of the upper and lower half bridges of the jth submodule of the kth phase, respectively. 、 are the fundamental frequency contents of the upper and lower half-bridge DC sides of the kth phase, 、 They are the maximum fundamental frequency content and the minimum fundamental frequency content respectively.

[0026] Preferably, the method of performing harmonic optimization on the target scalable cascade H-bridge energy storage system by utilizing the optimal doubled frequency circulating current and the optimal bias voltage further includes:

[0027] Comparing the fundamental frequency content obtained after harmonic optimization with a preset fundamental frequency content threshold, and judging whether the harmonic effect of the target scalable cascade H-bridge energy storage system meets predetermined requirements based on the comparison result;

[0028] If it is determined that the harmonic effect of the target scalable cascade H-bridge energy storage system does not meet the predetermined requirement, the method proceeds to the step of injecting an initial doubled frequency circulating current into the target scalable cascade H-bridge energy storage system and determining the DC side current of the target scalable cascade H-bridge energy storage system in combination with the initial bias voltage, based on the optimal doubled frequency circulating current and the optimal bias voltage, until the harmonic effect of the target scalable cascade H-bridge energy storage system meets the predetermined requirement.

[0029] In a second aspect, the present invention further provides a harmonic optimization system based on double frequency circulating current injection, comprising:

[0030] a circulating current injection module, configured to inject an initial doubled frequency circulating current into a target scalable cascade H-bridge energy storage system, update the three-phase current of the target scalable cascade H-bridge energy storage system, and determine the DC side current of the target scalable cascade H-bridge energy storage system based on the three-phase current combined with the initial bias voltage;

[0031] a fundamental wave content determination module, configured to extract a DC component and a fundamental wave component from the DC side current, and determine the fundamental wave content in the DC side current of each phase of the target scalable cascade H-bridge energy storage system based on the DC component and the fundamental wave component;

[0032] A model building module is used to build a harmonic optimization model with the minimization of the mean value of the fundamental wave content in the DC side current of each phase as the optimization goal and the limit value of the difference of the fundamental wave content of the DC side of each phase as the constraint condition;

[0033] A model optimization module is used to optimize and solve the harmonic optimization model, and determine the optimal double frequency circulating current and the optimal bias voltage according to the optimal solution;

[0034] A harmonic optimization module is used to perform harmonic optimization on the target scalable cascade H-bridge energy storage system using the optimal doubled frequency circulating current and the optimal bias voltage.

[0035] In a third aspect, the present invention further provides an electronic device comprising a memory and a processor, wherein a computer program is stored in the memory, and when the computer program is executed by the processor, the processor executes the steps of the harmonic optimization method based on double frequency circulating current injection as described in the first aspect.

[0036] In a fourth aspect, the present invention further provides a computer-readable storage medium having a computer program stored thereon, which, when executed, implements the steps of the harmonic optimization method based on double frequency circulating current injection as described in the first aspect.

[0037] In a fifth aspect, the present invention also provides a computer program product, comprising a computer program stored on a non-transitory computer-readable storage medium, wherein the computer program comprises program instructions, wherein when the program instructions are executed by a computer, the computer is caused to execute the steps of the harmonic optimization method based on double frequency circulating current injection as described in the first aspect.

[0038] As can be seen from the above technical solutions, the present invention injects an initial doubled frequency circulating current into the target scalable cascade H-bridge energy storage system, updates the three-phase current, and determines the DC side current of the target scalable cascade H-bridge energy storage system in combination with the initial bias voltage. The DC component and fundamental component in the DC side current are extracted, and the fundamental content in the DC side current of each phase of the target scalable cascade H-bridge energy storage system is determined based on the DC component and the fundamental component. The fundamental content in the DC side current of each phase of the target scalable cascade H-bridge energy storage system is minimized with the mean value of the fundamental content in the DC side current of each phase as the optimization goal, and the difference limit of the fundamental content of the DC side of each phase is used as a constraint condition to construct a harmonic optimization model. By using the constructed harmonic optimization model and the optimal parameters obtained by solving the solution, the injection of the doubled frequency circulating current and the bias voltage can be accurately controlled, so that the harmonic content in the DC side current of the target scalable cascade H-bridge energy storage system is minimized, which not only improves the performance of the system, but also ensures the balance between the DC side currents of each phase, avoiding problems such as equipment damage or unstable operation caused by excessive harmonic content. In addition, this harmonic optimization method has broad application prospects and can be applied to different types of cascaded H-bridge energy storage systems, providing a strong technical guarantee for the stable operation of the power system. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0040] Figure 1 This is a topology diagram of the exCHB-ESS energy storage system provided by an embodiment of the present invention;

[0041] Figure 2 The exCHB-ESS submodule topology diagram provided in an embodiment of the present invention;

[0042] Figure 3A diagram illustrating an application environment of a harmonic optimization method based on double frequency circulating current injection provided by an embodiment of the present invention;

[0043] Figure 4 A flowchart of a harmonic optimization method based on double frequency circulating current injection provided by an embodiment of the present invention;

[0044] Figure 5 A control block diagram of a method for injecting circulating current to suppress fundamental components provided by an embodiment of the present invention;

[0045] Figure 6 A waveform diagram of the circulating current during the first simulation injection provided by an embodiment of the present invention;

[0046] Figure 7 A comparison diagram of the DC side fundamental wave suppression effect of the first simulation provided by an embodiment of the present invention;

[0047] Figure 8 The circulating current waveform of the second simulation injection provided by the embodiment of the present invention;

[0048] Figure 9 A comparison diagram of the DC side fundamental wave suppression effect of the second simulation provided by an embodiment of the present invention;

[0049] Figure 10 The circulating current waveform of the third simulation injection provided by the embodiment of the present invention;

[0050] Figure 11 A comparison diagram of the DC side fundamental wave suppression effect of the third simulation provided by an embodiment of the present invention;

[0051] Figure 12 The circulating current waveform of the fourth simulation injection provided by the embodiment of the present invention;

[0052] Figure 13 A comparison diagram of the DC side fundamental wave suppression effect of the fourth simulation provided by an embodiment of the present invention;

[0053] Figure 14 A schematic structural diagram of a harmonic optimization system based on double frequency circulating current injection provided by an embodiment of the present invention;

[0054] Figure 15 A schematic structural diagram of an electronic device provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0055] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of 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 making creative efforts shall fall within the scope of protection of the present invention.

[0056] The harmonic optimization method based on double frequency circulating current injection provided in the embodiment of the present application can be applied to Figure 3 In the application environment shown, the terminal 101 communicates with the server 102 via a network. The data storage system can store data that the server 102 needs to process. The data storage system can be integrated on the server 102 or placed on the cloud or other network servers. The terminal 101 or the server 102 injects an initial double frequency circulating current into the target scalable cascade H-bridge energy storage system, updates the three-phase current of the target scalable cascade H-bridge energy storage system, and determines the DC side current of the target scalable cascade H-bridge energy storage system based on the three-phase current and the initial bias voltage; extracts the DC component and the fundamental component in the DC side current, and determines the fundamental content in the DC side current of each phase of the target scalable cascade H-bridge energy storage system based on the DC component and the fundamental component; constructs a harmonic optimization model with minimizing the mean value of the fundamental content in the DC side current of each phase as an optimization goal and with the difference limit of the fundamental content of the DC side of each phase as a constraint condition; seeks an optimal solution for the harmonic optimization model, and determines the optimal double frequency circulating current and the optimal bias voltage based on the optimal solution; and uses the optimal double frequency circulating current and the optimal bias voltage to perform harmonic optimization on the target scalable cascade H-bridge energy storage system.

[0057] The terminal 101 may be, but is not limited to, various personal computers, laptops, smart phones, tablet computers, and the like.

[0058] The server 102 may be an independent physical server, a server cluster or a distributed system composed of multiple physical servers, or a cloud server that provides cloud computing services.

[0059] like Figure 4 As shown, the embodiment of the present application provides a harmonic optimization method based on double frequency circulating current injection, and the method is applied to Figure 3 The terminal 101 or the server 102 in the embodiment is used as an example to illustrate the method, which includes the following steps S1 to S5.

[0060] Step S1: injecting an initial doubled frequency circulating current into a target scalable cascade H-bridge energy storage system, updating the three-phase current of the target scalable cascade H-bridge energy storage system, and determining the DC side current of the target scalable cascade H-bridge energy storage system based on the three-phase current combined with the initial bias voltage.

[0061] The doubled-frequency circulating current is a current component with a frequency twice that of the grid's fundamental frequency. By injecting the initial doubled-frequency circulating current into the target scalable cascaded H-bridge energy storage system (exCHB-ESS), the current distribution in the system can be effectively changed, thereby affecting the harmonic components.

[0062] In order to effectively suppress the harmonic components in the DC side current of the target scalable cascade H-bridge energy storage system, after injecting the doubled frequency circulating current, the system's three-phase current will be updated accordingly. The updated three-phase current is combined with the given initial bias voltage to calculate the DC side current of the target scalable cascade H-bridge energy storage system.

[0063] Step S2: extracting the DC component and fundamental component in the DC side current, and determining the fundamental content in the DC side current of each phase of the target scalable cascade H-bridge energy storage system according to the DC component and the fundamental component.

[0064] The DC component is the constant component of the DC side current, while the fundamental component is the current component with the same fundamental frequency as the grid. Spectral analysis of the DC side current accurately extracts the DC and fundamental components. The extracted DC and fundamental components are then used to determine the fundamental content of the DC side current in each phase of the target scalable cascaded H-bridge energy storage system, thereby assessing the harmonics in each phase of the DC side current.

[0065] In practical applications, the level of harmonic content directly affects power quality and equipment efficiency. By accurately calculating the fundamental wave content, we can further analyze the harmonic components and provide key data support for subsequent optimization steps.

[0066] Step S3: construct a harmonic optimization model with minimizing the mean value of the fundamental wave content in the DC side current of each phase as the optimization goal and with the difference limit of the fundamental wave content of each phase DC side as the constraint condition.

[0067] To effectively suppress the harmonic components in the DC side current, the fundamental wave content in each phase of the DC side current should be as small as possible. Therefore, the embodiment of the present application takes minimizing the mean value of the fundamental wave content in each phase of the DC side current as the optimization goal, and uses the difference limit of the fundamental wave content of each phase of the DC side as a constraint condition, thereby taking into account the balance between the DC side currents of each phase. When constructing the harmonic optimization model, the actual operating conditions and optimization requirements of the target scalable cascade H-bridge energy storage system were comprehensively considered to ensure the accuracy and feasibility of the optimization results.

[0068] Step S4: finding an optimal solution for the harmonic optimization model, and determining an optimal double frequency circulating current and an optimal bias voltage according to the optimal solution.

[0069] The harmonic optimization model can be solved using a mathematical solver. By optimizing the harmonic optimization model, parameters related to the double-frequency circulating current and bias voltage can be obtained, and then the optimal double-frequency circulating current and bias voltage can be determined using these parameters. These parameters are key to achieving harmonic optimization, effectively suppressing the harmonic components in the DC-side current of the target scalable cascaded H-bridge energy storage system while maintaining the balance between the DC-side currents of each phase.

[0070] Step S5: Harmonic optimization is performed on the target scalable cascade H-bridge energy storage system using the optimal doubled frequency circulating current and the optimal bias voltage.

[0071] After determining the optimal double-frequency circulating current and bias voltage, these can be used to perform harmonic optimization on the target scalable cascaded H-bridge energy storage system. By adjusting the double-frequency circulating current and bias voltage in the system, harmonic components in the DC side current can be effectively suppressed, thereby improving the system's power quality and operating efficiency.

[0072] It should be noted that the embodiment of the present application injects an initial doubled frequency circulating current into the target scalable cascade H-bridge energy storage system and updates the three-phase current. In combination with the initial bias voltage, the DC side current of the target scalable cascade H-bridge energy storage system is determined, the DC component and the fundamental component in the DC side current are extracted, and the fundamental content in the DC side current of each phase of the target scalable cascade H-bridge energy storage system is determined based on the DC component and the fundamental component. The fundamental content in the DC side current of each phase of the target scalable cascade H-bridge energy storage system is minimized with the mean value of the fundamental content in the DC side current of each phase as the optimization goal, and the difference limit of the fundamental content of the DC side of each phase is used as a constraint condition to construct a harmonic optimization model. By using the constructed harmonic optimization model and the optimal parameters obtained by solving the solution, the injection of the doubled frequency circulating current and the bias voltage can be accurately controlled, so that the harmonic content in the DC side current of the target scalable cascade H-bridge energy storage system is minimized, which not only improves the performance of the system, but also ensures the balance between the DC side currents of each phase, avoiding problems such as equipment damage or unstable operation caused by excessive harmonic content. In addition, this harmonic optimization method has broad application prospects and can be applied to different types of cascaded H-bridge energy storage systems, providing a strong technical guarantee for the stable operation of the power system.

[0073] In some embodiments, injecting an initial doubled frequency circulating current into a target scalable cascade H-bridge energy storage system, updating a three-phase current of the target scalable cascade H-bridge energy storage system, and determining a DC side current of the target scalable cascade H-bridge energy storage system based on the three-phase current combined with an initial bias voltage includes:

[0074] Step S101: injecting an initial doubled frequency circulating current into a delta-connected circuit of a target scalable cascaded H-bridge energy storage system to obtain a three-phase current after superimposing the doubled frequency circulating current.

[0075] Among them, such as Figure 1 As shown, since the triangle-connected circuit of the target scalable cascade H-bridge energy storage system is internally a triangle loop, the current of all phases of the target scalable cascade H-bridge energy storage system can be updated by injecting the initial doubled frequency circulating current into the triangle-connected circuit of the target scalable cascade H-bridge energy storage system, as shown in FIG. Figure 5 As shown, an initial doubled frequency circulating current is injected into the delta-connected circuit of a target scalable cascaded H-bridge energy storage system. The amplitude and phase angle of the injected circulating current are manually set. A PR controller then generates a corresponding zero-sequence voltage. This zero-sequence voltage is superimposed on the modulated wave to generate a circulating current within the delta circuit of the energy storage system. This approach not only reduces power fluctuations during battery operation and extends its service life, but also significantly reduces the required series inductance of the power branch, thereby reducing the overall system size and manufacturing cost.

[0076] In the specific implementation, Figure 5 As shown, first determine the phase angle of the circulating current to be injected and circulation amplitude After that, the given value of the circulation can be formed Then set the given value of the circulation and the sampling value of the circulation Compare and subtract to get the deviation value of circulation Finally, the deviation value is inverted and input into the PR controller to obtain the zero-sequence voltage to be injected. , superimposing this zero-sequence voltage on the modulation wave can generate the required circulating current.

[0077] In an example, when the exCHB-ESS exports power to the grid, the voltage and current on the jth submodule without the initial double frequency circulating current can be expressed as:

[0078]

[0079]

[0080]

[0081] in, is the upper half-bridge output voltage of the jth submodule, is the output voltage of the lower half-bridge of the jth submodule, Indicates the submodule voltage amplitude, Represents the angular relationship between three-phase symmetrical alternating currents, is the fundamental current amplitude, is the phase angle of the fundamental current relative to the ab phase voltage, is the grid voltage angular velocity, and k represents the phase index.

[0082] At this time, a double frequency circulating current is injected into the circuit of the energy storage system in a triangle connection. :

[0083]

[0084] Where, is the circulation amplitude, is the phase angle.

[0085] Therefore, the three-phase current after superimposing the double frequency circulating current is expressed as:

[0086]

[0087] Where, It is the three-phase current after double frequency circulation.

[0088] Step S102 : determining the bias-modulated AC side output voltage according to the target scalable cascade H-bridge energy storage system's AC side output voltage and the initial bias voltage.

[0089] Among them, the AC side output voltage is generally expressed as , and then superimpose the initial bias voltage After that, the AC side output voltage after bias modulation can be obtained, as shown in wait.

[0090] Step S103 : determining the switching functions of the upper and lower half bridges of each phase and each submodule according to the bias-modulated AC side output voltage and the target DC side voltage of the scalable cascaded H-bridge energy storage system.

[0091] The switching functions of the upper and lower half-bridges of each phase and submodule are used to control the switching states of each phase and submodule, thereby achieving precise control of the target scalable cascade H-bridge energy storage system. By properly designing the switching function, the AC-side output voltage after bias modulation can be matched to the DC-side voltage, ensuring stable system operation. The design of the switching function must take into account the actual operating conditions and optimization requirements of the system to ensure the accuracy and feasibility of the optimization results. During implementation, the switching function can be flexibly adjusted based on the specific parameters and operating conditions of the target scalable cascade H-bridge energy storage system to meet the actual needs of the system.

[0092] In the embodiment of the present application, the switching functions of the upper and lower half bridges of each phase and each submodule are determined by the ratio of the AC side output voltage after bias modulation to the DC side voltage of the target scalable cascade H-bridge energy storage system:

[0093]

[0094]

[0095]

[0096] Where, is the DC side voltage of the submodule, They are the switching functions of the upper and lower half-bridges of the j-th sub-module of phase k, respectively.

[0097] In order to prevent the system from overmodulation, the switching function values ​​of the upper and lower half bridges of each phase and each submodule are between 0 and 1, that is:

[0098]

[0099] Step S104 : Determine the DC side current of the target expandable cascade H-bridge energy storage system based on the switching functions of the upper and lower half bridges of each phase and each submodule and the three-phase current after superposition of the doubled frequency circulating current.

[0100] The DC side current of the target scalable cascaded H-bridge energy storage system is obtained by multiplying the switching functions of the upper and lower half-bridges of each phase and each sub-module with the three-phase current after superimposing the doubled frequency circulating current:

[0101]

[0102] in, is the DC side current of phase k.

[0103] In some embodiments, extracting a DC component and a fundamental component from the DC side current, and determining the fundamental content of the DC side current of each phase of the target scalable cascade H-bridge energy storage system based on the DC component and the fundamental component, includes:

[0104] Step S201 : extracting the DC component and the fundamental wave component in the DC side current, and determining the DC component amplitude and the fundamental wave component amplitude respectively.

[0105] Among them, after the DC side current of the target cascade H-bridge energy storage system is expanded, the current expansion formula of each phase DC side can be obtained through product and difference, and the current components of the DC side can be analyzed from it:

[0106]

[0107] By analyzing the expansion, we can know that the DC side of the submodule contains the fundamental frequency component (including All items of All items), triple frequency components (including all terms) and DC components (excluding all items in the .

[0108] In the above formula, there is only one term without , so the direct current component amplitude in the direct current side current can be directly represented as follows:

[0109]

[0110]

[0111] wherein, is the direct current in the direct current side of the upper and lower half-bridges of each submodule of the k phase.

[0112] The fundamental component (including ) in the direct current side current is as follows:

[0113]

[0114]

[0115] wherein, is the fundamental frequency current in the direct current side of the upper and lower half-bridges of each submodule of the k phase.

[0116] From the above formula, it can be seen that the fundamental component of the direct current side current is composed of the addition of two fundamental frequency cosine functions, and the amplitude of the superposition of any two cosine functions can be calculated according to the following formula:

[0117]

[0118] In the formula, A1 and A2 represent the amplitude terms of the fundamental component.

[0119] Therefore, the amplitude of the fundamental component in the direct current side of the upper and lower layer half-bridges of the k phase can be represented as follows in combination with the above formula:

[0120]

[0121]

[0122] In step S202, the ratio of the amplitude of the fundamental component to the amplitude of the direct current component is operated to determine the fundamental content in the direct current side current of each phase of the target scalable cascaded H-bridge energy storage system.

[0123] wherein the fundamental content in the direct current side current of each phase can be represented as the ratio of the amplitude of the direct current side fundamental component to the amplitude of the direct current component:

[0124]

[0125] wherein, respectively, the fundamental content in the direct current side of the upper and lower layer half-bridges of the k phase.

[0126] In some embodiments, the objective function corresponding to the optimization objective is:

[0127] Where, is the mean value of the fundamental wave content in the DC side current of each phase, is the amplitude of the double frequency circulating current, is the double frequency circulation phase angle, is the bias voltage of ab phase, is the bias voltage of phase bc, is the bias voltage of the ca phase, 、 are the fundamental frequency contents of the upper and lower half-bridge DC sides of the ab phases, 、 are the fundamental frequency contents of the upper and lower half-bridge DC sides of phase bc, respectively. 、 are the fundamental frequency contents of the upper and lower half-bridge DC sides of phase ca, respectively;

[0128] The constraints are:

[0129]

[0130] Where, 、 are the switching functions of the upper and lower half bridges of the jth submodule of the kth phase, respectively. 、 are the fundamental frequency contents of the upper and lower half-bridge DC sides of the kth phase, 、 They are the maximum fundamental frequency content and the minimum fundamental frequency content respectively.

[0131] Among them, the fundamental wave content expression of the DC side current of the upper and lower half-bridges of each phase is The signs and angles are different, so consider injecting a suitable double frequency circulating current to minimize the average value of the fundamental wave content on the DC side of each phase while keeping the difference in the fundamental wave content on the DC side of each phase within 10%.

[0132] Under the above constraints, solve the relevant parameters of the double frequency circulating current and bias voltage , by changing the five independent variables, thus affecting Finally, the above optimization problem is solved by traversal algorithm in Matlab, and a minimum value of the average value of the fundamental wave content on the DC side is obtained. The circulating current and bias voltage are the optimal circulating current and the optimal bias voltage.

[0133] In some embodiments, harmonic optimization is performed on a target scalable cascade H-bridge energy storage system using an optimal doubled frequency circulating current and an optimal bias voltage, and then further comprising:

[0134] Step S601: Compare the fundamental frequency content obtained after harmonic optimization with a preset fundamental frequency content threshold, and determine whether the harmonic effect of the target scalable cascade H-bridge energy storage system meets predetermined requirements based on the comparison result.

[0135] The fundamental frequency content threshold can be set through simulation. If the fundamental frequency content obtained after harmonic optimization is lower than the preset fundamental frequency content threshold, it means that the harmonic effect of the target scalable cascade H-bridge energy storage system has met or exceeded the predetermined requirements, and the system has high operating efficiency and stability. Conversely, if the fundamental frequency content after harmonic optimization is higher than the preset fundamental frequency content threshold, it means that the harmonic effect of the target scalable cascade H-bridge energy storage system has not yet met the predetermined requirements. In this case, it is necessary to further adjust the optimization parameters and re-perform harmonic optimization until the predetermined requirements are met. Through such comparison and judgment, it can be ensured that the harmonic optimization effect of the target scalable cascade H-bridge energy storage system reaches the optimal state, thereby improving the overall performance and reliability of the system.

[0136] Step S602: If it is determined that the harmonic effect of the target scalable cascade H-bridge energy storage system does not meet the predetermined requirements, then, based on the optimal doubled frequency circulating current and the optimal bias voltage, the process proceeds to the step of injecting an initial doubled frequency circulating current into the target scalable cascade H-bridge energy storage system, and determining the DC side current of the target scalable cascade H-bridge energy storage system in combination with the initial bias voltage, until the harmonic effect of the target scalable cascade H-bridge energy storage system meets the predetermined requirements.

[0137] To demonstrate the effectiveness of the proposed harmonic optimization method based on double-frequency circulating current injection, we use MATLAB / Simulink and a specific simulation example to further illustrate and verify the method. The exCHB-ESS system parameters are given in Table 1.

[0138] Table 1: exCHB-ESS system parameters

[0139]

[0140] In this example, a total of 4 simulations were designed. First, in order to reflect the three variables The design only changes the amplitude of the injected circulation Simulation, only changing the phase angle of the injection circulation Simulation and changing only the bias voltage The simulations are repeated to verify the effect of each variable on the fundamental component, which are recorded as the first simulation, the second simulation, and the third simulation. Finally, the simulation of injecting the optimal circulating current is designed to verify the effect of the optimal injected circulating current and setting the optimal voltage bias on the fundamental component, which is recorded as the fourth simulation.

[0141] A method for suppressing the fundamental component of the DC side of a cascaded H-bridge energy storage system with injected circulating current based on Simulink / Matlab. Figure 6-7 The first simulation results are given; Figure 8-9 The second simulation results are given; Figure 10-11 The third simulation results are given; Figure 12-13 The fourth simulation results are given.

[0142] The specific simulation situation is as follows:

[0143] Table 2: Design of the first simulation condition

[0144]

[0145] In the first simulation, only the amplitude of the injected circulating current is changed without changing the injected circulating current phase angle and bias voltage, which mainly reflects the impact of the injected circulating current amplitude on the fundamental wave content of the DC side. Figure 6 As shown, Figure 6 The horizontal axis represents time t, and the vertical axis represents the amplitude of the injected circulating current. At t=0s, the system enters operating condition 1, the system operates normally, and no circulating current is injected; at t=0.2s, the system enters operating condition 2, the injected voltage amplitude is 10A, the phase angle is 0°, and the three phases use a bias voltage of 800V; at t=0.4s, the system enters operating condition 3, the injected voltage amplitude is 20A, the phase angle is 0°, and the three phases use a bias voltage of 800V; at t=0.6s, the system enters operating condition 4, the injected voltage amplitude is 30A, the phase angle is 0°, and the three phases use a bias voltage of 800V; at t=0.8s, the system enters operating condition 5, the injected voltage amplitude is 40A, the phase angle is 0°, and the three phases use a bias voltage of 800V.

[0146] in, Figure 7 The simulation results shown are Figure 7 The horizontal axis represents the DC side fundamental wave index, and the vertical axis represents the DC side fundamental wave content. By changing the amplitude of the injected circulating current, the size of the DC side fundamental wave content can be changed to a certain extent.

[0147] In the second simulation, only the phase angle of the injected circulating current is changed without changing the amplitude and bias voltage of the injected circulating current, which mainly reflects the influence of the phase angle of the injected circulating current on the fundamental wave content of the DC side. Figure 8 As shown in Table 3, Figure 8The middle horizontal coordinate represents time t, and the vertical coordinate represents the amplitude of the injected circulating current. At t=0s, the system enters working condition 1, and the system is normally operated without injecting a circulating current. At t=0.2s, the system enters working condition 2, the amplitude of the injected circulating current is 20A, the phase angle is 45°, and 800V bias voltage is used for three phases. At t=0.4s, the system enters working condition 3, the amplitude of the injected voltage is 20A, the phase angle is 90°, and 800V bias voltage is used for three phases. At t=0.6s, the system enters working condition 4, the amplitude of the injected voltage is 20A, the phase angle is 135°, and 800V bias voltage is used for three phases. At t=0.8s, the system enters working condition 5, the amplitude of the injected voltage is 20A, the phase angle is 180°, and 800V bias voltage is used for three phases.

[0148] Table 3: Second simulation working condition design

[0149]

[0150] wherein, Figure 9 The simulation results shown in Table 3 show that, Figure 9 The middle horizontal coordinate represents the DC side fundamental index, and the vertical coordinate represents the DC side fundamental content. By changing the phase angle of the injected circulating current, the suppression effect of the circulating current on the DC side voltage fundamental content of different phases can be affected. Therefore, as long as the angle of the injected voltage is appropriate, the suppression effect of the injected voltage on the DC side voltage fundamental content can be optimized.

[0151] In the third simulation, only the size of the DC bias voltage is changed, and the amplitude and phase angle of the injected circulating current are not changed, mainly reflecting the influence of the DC bias on the DC side fundamental content. As shown in Table 4 and Table 5, Figure 10 and Table 4 show that, Figure 10 The middle horizontal coordinate represents time t, and the vertical coordinate represents the amplitude of the injected circulating current. At t=0s, the system enters working condition 1, and the system is normally operated without injecting a circulating current. At t=0.2s, the system enters working condition 2, the amplitude of the injected circulating current is 20A, the phase angle is 45°, and 800V bias voltage is used for three phases. At t=0.4s, the system enters working condition 3, the amplitude of the injected circulating current is 20A, the phase angle is 90°, and 800V bias voltage is used for three phases. At t=0.6s, the system enters working condition 4, the amplitude of the injected circulating current is 20A, the phase angle is 135°, and 800V bias voltage is used for three phases. At t=0.8s, the system enters working condition 5, the amplitude of the injected circulating current is 20A, the phase angle is 180°, and 800V bias voltage is used for three phases.

[0152] Table 4: Third simulation working condition design

[0153]

[0154] Figure 11 The simulation results shown in Table 3 show that, Figure 11The horizontal axis represents the DC side fundamental wave index, and the vertical axis represents the DC side fundamental wave content. By reducing the magnitude of the DC voltage bias, the magnitude of the fundamental wave component can be effectively suppressed.

[0155] In the fourth simulation, the injection of optimal circulating current and the setting of optimal bias voltage are considered, which mainly reflects the suppression effect of the fundamental wave component of the DC side by the simultaneous coordination of the five variables. Figure 12 As shown in Table 5, Figure 12 The horizontal axis represents time t, and the vertical axis represents the amplitude of the injected circulating current. At t=0s, the system enters working condition 1, the system operates normally, no voltage is injected, and a bias voltage of 800V is used; at t=0.2s, the system enters working condition 2, the injected circulating current amplitude is 4A, the phase angle is 180°, and the three phases all use a bias voltage of 550V. At this time, the optimal circulating current and optimal bias voltage are obtained by the traversal algorithm, and the corresponding theoretical minimum fundamental content average value should be .

[0156] Table 5: Design of the fourth simulation condition

[0157]

[0158] Figure 13 The simulation results shown show that Figure 13 The horizontal axis represents the DC side fundamental wave index, and the vertical axis represents the DC side fundamental wave content. The battery side harmonic optimization method proposed in this application can effectively reduce the fundamental wave content of the exCHB-ESS submodule DC side by injecting appropriate double frequency circulating current and coordinating it with DC voltage bias. At the same time, the minimum fundamental wave content average value obtained by simulation is The average value of the fundamental content calculated by the algorithm They are almost consistent, indicating that the optimal injected circulating current and the optimal bias voltage can be solved through programming algorithms to minimize the fundamental wave content on the DC side.

[0159] Based on the same inventive concept, an embodiment of the present application further provides a harmonic optimization system based on double frequency circulating current injection for implementing the above-mentioned harmonic optimization method based on double frequency circulating current injection.

[0160] The implementation solution provided by the system to solve the problem is similar to the implementation solution described in the above method. Therefore, the specific limitations in one or more embodiments of the harmonic optimization system based on double frequency circulating current injection provided below can be found in the above limitations on the harmonic optimization method based on double frequency circulating current injection, and will not be repeated here.

[0161] like Figure 14 As shown, the embodiment of the present application provides a harmonic optimization system based on double frequency circulating current injection, including:

[0162] The circulating current injection module 100 is used to inject an initial doubled frequency circulating current into the target scalable cascade H-bridge energy storage system, update the three-phase current of the target scalable cascade H-bridge energy storage system, and determine the DC side current of the target scalable cascade H-bridge energy storage system based on the three-phase current combined with the initial bias voltage;

[0163] A fundamental content determination module 200 is configured to extract the DC component and the fundamental component from the DC side current, and determine the fundamental content of the DC side current of each phase of the target scalable cascade H-bridge energy storage system based on the DC component and the fundamental component;

[0164] The model building module 300 is used to build a harmonic optimization model with minimization of the mean value of the fundamental wave content in the DC side current of each phase as the optimization goal and with the difference limit of the fundamental wave content of the DC side of each phase as the constraint condition;

[0165] The model optimization module 400 is used to optimize and solve the harmonic optimization model and determine the optimal double frequency circulating current and the optimal bias voltage according to the optimal solution;

[0166] The harmonic optimization module 500 is used to perform harmonic optimization on the target scalable cascade H-bridge energy storage system using the optimal double frequency circulating current and the optimal bias voltage.

[0167] In some embodiments, the circulating injection module 100 is configured to:

[0168] Injecting an initial doubled frequency circulating current into the delta-connected circuit of the target scalable cascade H-bridge energy storage system to obtain a three-phase current after superimposing the doubled frequency circulating current;

[0169] Determine the AC side output voltage after bias modulation based on the target scalable cascade H-bridge energy storage system's AC side output voltage and initial bias voltage;

[0170] Determine the switching functions of the upper and lower half-bridges of each phase and each submodule based on the AC side output voltage after bias modulation and the DC side voltage of the target scalable cascade H-bridge energy storage system;

[0171] The DC side current of the target scalable cascade H-bridge energy storage system is determined based on the switching functions of the upper and lower half bridges of each phase and each sub-module and the three-phase current after superimposing the doubled frequency circulating current.

[0172] In some embodiments, the switching function values ​​of the upper and lower half bridges of each phase and each sub-module are between 0 and 1.

[0173] In some embodiments, the fundamental content determination module 200 is configured to:

[0174] Extracting the DC component and fundamental component in the DC side current, and determining the DC component amplitude and the fundamental component amplitude respectively;

[0175] According to the ratio operation of the fundamental component amplitude and the DC component amplitude, the fundamental content in the DC side current of each phase of the target scalable cascade H-bridge energy storage system is determined.

[0176] In some embodiments, the objective function corresponding to the optimization objective is:

[0177] Where, is the mean value of the fundamental wave content in the DC side current of each phase, is the amplitude of the double frequency circulating current, is the double frequency circulation phase angle, is the bias voltage of the ab phase, is the bias voltage of phase bc, is the bias voltage of the ca phase, 、 are the fundamental frequency contents of the upper and lower half-bridge DC sides of the ab phases, 、 are the fundamental frequency contents of the upper and lower half-bridge DC sides of phase bc, respectively. 、 are the fundamental frequency contents of the upper and lower half-bridge DC sides of phase ca, respectively;

[0178] The constraints are:

[0179]

[0180] Where, 、 are the switching functions of the upper and lower half bridges of the jth submodule of the kth phase, respectively. 、 are the fundamental frequency contents of the upper and lower half-bridge DC sides of the kth phase, 、 They are the maximum fundamental frequency content and the minimum fundamental frequency content respectively.

[0181] In some embodiments, the system further comprises:

[0182] An optimization module is used to compare the fundamental frequency content obtained after harmonic optimization with a preset fundamental frequency content threshold, and determine whether the harmonic effect of the target scalable cascade H-bridge energy storage system meets the predetermined requirements based on the comparison result;

[0183] When it is determined that the harmonic effect of the target scalable cascade H-bridge energy storage system does not meet the predetermined requirements, the step of injecting an initial doubled frequency circulating current into the target scalable cascade H-bridge energy storage system according to the optimal doubled frequency circulating current and the optimal bias voltage, and determining the DC side current of the target scalable cascade H-bridge energy storage system in combination with the initial bias voltage, until the harmonic effect of the target scalable cascade H-bridge energy storage system meets the predetermined requirements.

[0184] like Figure 15 As shown, an embodiment of the present application provides an electronic device, the electronic device 10 includes a memory 20 and a processor 30, the memory 20 stores a computer program, and when the computer program is executed by the processor 30, the processor 30 performs the steps of the harmonic optimization method based on double frequency circulating current injection as in the above embodiment.

[0185] An embodiment of the present application provides a computer-readable storage medium having a computer program stored thereon. When the computer program is executed, the steps of the harmonic optimization method based on double frequency circulating current injection as described in the above embodiment are implemented.

[0186] An embodiment of the present application provides a computer program product, which includes a computer program stored on a non-transitory computer-readable storage medium, and the computer program includes program instructions. When the program instructions are executed by a computer, the computer performs the steps of the harmonic optimization method based on double frequency circulating current injection as described in the above embodiment.

[0187] Those skilled in the art will clearly understand that, for the convenience and brevity of description, the specific working processes of the above-described systems, electronic devices, computer storage media, and computer program products can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0188] It should be noted that the terms "including" and "having" and any variations thereof in the specification and claims of the present invention and the above-mentioned drawings are intended to cover non-exclusive inclusions. For example, a process, method, system, product or apparatus comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or are inherent to these processes, methods, products or apparatuses.

[0189] It should be understood that, although the various steps in the flowcharts involved in the above embodiments are shown in sequence as indicated by the arrows, these steps are not necessarily performed in sequence in the order indicated by the arrows. Unless otherwise specified herein, there is no strict order restriction on the execution of these steps, and these steps can be performed in other orders. Moreover, at least a portion of the steps in the flowcharts involved in the above embodiments may include multiple steps or multiple stages, and these steps or stages are not necessarily performed at the same time, but can be performed at different times, and the execution order of these steps or stages is not necessarily performed in sequence, but can be performed in turn or alternately with other steps or at least a portion of steps or stages in other steps.

[0190] In the several embodiments provided by the present invention, it should be understood that the disclosed systems, electronic devices, computer storage media, computer program products and methods can be implemented in other ways. For example, the device embodiments described above are merely schematic. For example, the division of the units is merely a logical function division. In actual implementation, there may be other division methods, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be an indirect coupling or communication connection through some interfaces, devices or units, which can be electrical, mechanical or other forms.

[0191] The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of these units may be selected to achieve the purpose of this embodiment according to actual needs.

[0192] In addition, the functional units in the various embodiments of the present invention may be integrated into a single processing unit, each unit may exist physically separately, or two or more units may be integrated into a single unit. The aforementioned integrated units may be implemented in the form of hardware or software functional units.

[0193] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the portion that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions for executing all or part of the steps of the method described in each embodiment of the present invention via a computer device (which can be a personal computer, server, or network device, etc.). The aforementioned storage medium includes various media that can store program code, such as a USB flash drive, a mobile hard drive, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk.

[0194] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A harmonic optimization method based on double frequency circulating current injection, characterized in that: include: Injecting an initial doubled frequency circulating current into a target scalable cascade H-bridge energy storage system, updating the three-phase current of the target scalable cascade H-bridge energy storage system, and determining the DC side current of the target scalable cascade H-bridge energy storage system based on the three-phase current combined with the initial bias voltage; Extracting a DC component and a fundamental component from the DC side current, and determining a fundamental content in the DC side current of each phase of the target scalable cascade H-bridge energy storage system based on the DC component and the fundamental component; The harmonic optimization model is constructed with the minimization of the mean value of the fundamental wave content in the DC side current of each phase as the optimization goal and the limit of the difference of the fundamental wave content of each phase DC side as the constraint condition. Finding an optimal solution for the harmonic optimization model, and determining an optimal double frequency circulating current and an optimal bias voltage according to the optimal solution; Harmonic optimization is performed on the target scalable cascade H-bridge energy storage system using the optimal doubled frequency circulating current and the optimal bias voltage.

2. The harmonic optimization method based on double frequency circulating current injection according to claim 1, characterized in that: The step of injecting an initial doubled frequency circulating current into the target scalable cascade H-bridge energy storage system, updating the three-phase current of the target scalable cascade H-bridge energy storage system, and determining the DC side current of the target scalable cascade H-bridge energy storage system based on the three-phase current combined with the initial bias voltage includes: Injecting an initial doubled frequency circulating current into a delta-connected circuit of the target scalable cascade H-bridge energy storage system to obtain a three-phase current after superimposing the doubled frequency circulating current; Determining the bias-modulated AC side output voltage according to the target scalable AC side output voltage of the cascaded H-bridge energy storage system and the initial bias voltage; Determining the switching functions of the upper and lower half bridges of each phase and each submodule according to the bias-modulated AC side output voltage and the DC side voltage of the target scalable cascade H-bridge energy storage system; The DC side current of the target expandable cascade H-bridge energy storage system is determined according to the switching functions of the upper and lower half bridges of each phase and each submodule and the three-phase current after the doubled frequency circulating current is superimposed.

3. The harmonic optimization method based on double frequency circulating current injection according to claim 2, characterized in that: The values ​​of the switching functions of the upper and lower half bridges of each phase and each submodule are between 0 and 1.

4. The harmonic optimization method based on double frequency circulating current injection according to claim 1, characterized in that: The extracting of the DC component and the fundamental component in the DC side current, and determining the fundamental content in the DC side current of each phase of the target scalable cascade H-bridge energy storage system according to the DC component and the fundamental component, includes: Extracting a DC component and a fundamental component from the DC side current, and determining the DC component amplitude and the fundamental component amplitude respectively; The fundamental content in the DC side current of each phase of the target expandable cascade H-bridge energy storage system is determined based on the ratio of the fundamental component amplitude to the DC component amplitude.

5. The harmonic optimization method based on double frequency circulating current injection according to claim 1 or 4, characterized in that: The objective function corresponding to the optimization objective is: Where, is the mean value of the fundamental wave content in the DC side current of each phase, is the amplitude of the double frequency circulating current, is the double frequency circulation phase angle, is the bias voltage of the ab phase, is the bias voltage of phase bc, is the bias voltage of the ca phase, 、 are the fundamental frequency contents of the upper and lower half-bridge DC sides of the ab phases, 、 are the fundamental frequency contents of the upper and lower half-bridge DC sides of phase bc, respectively. 、 are the fundamental frequency contents of the upper and lower half-bridge DC sides of phase ca, respectively; The constraints are: Where, 、 are the switching functions of the upper and lower half bridges of the jth submodule of the kth phase, respectively. 、 are the fundamental frequency contents of the upper and lower half-bridge DC sides of the kth phase, 、 They are the maximum fundamental frequency content and the minimum fundamental frequency content respectively.

6. The harmonic optimization method based on double frequency circulating current injection according to claim 1, characterized in that: The method further comprises performing harmonic optimization on the target scalable cascade H-bridge energy storage system by utilizing the optimal doubled frequency circulating current and the optimal bias voltage, and then further comprising: Comparing the fundamental frequency content obtained after harmonic optimization with a preset fundamental frequency content threshold, and judging whether the harmonic effect of the target scalable cascade H-bridge energy storage system meets predetermined requirements based on the comparison result; If it is determined that the harmonic effect of the target scalable cascade H-bridge energy storage system does not meet the predetermined requirement, the method proceeds to the step of injecting an initial doubled frequency circulating current into the target scalable cascade H-bridge energy storage system and determining the DC side current of the target scalable cascade H-bridge energy storage system in combination with the initial bias voltage, based on the optimal doubled frequency circulating current and the optimal bias voltage, until the harmonic effect of the target scalable cascade H-bridge energy storage system meets the predetermined requirement.

7. A harmonic optimization system based on double frequency circulating current injection, characterized in that: include: a circulating current injection module, configured to inject an initial doubled frequency circulating current into a target scalable cascade H-bridge energy storage system, update the three-phase current of the target scalable cascade H-bridge energy storage system, and determine the DC side current of the target scalable cascade H-bridge energy storage system based on the three-phase current combined with the initial bias voltage; a fundamental wave content determination module, configured to extract a DC component and a fundamental wave component from the DC side current, and determine the fundamental wave content in the DC side current of each phase of the target scalable cascade H-bridge energy storage system based on the DC component and the fundamental wave component; A model building module is used to build a harmonic optimization model with the minimization of the mean value of the fundamental wave content in the DC side current of each phase as the optimization goal and the limit value of the difference of the fundamental wave content of the DC side of each phase as the constraint condition; A model optimization module is used to optimize and solve the harmonic optimization model, and determine the optimal double frequency circulating current and the optimal bias voltage according to the optimal solution; A harmonic optimization module is used to perform harmonic optimization on the target scalable cascade H-bridge energy storage system using the optimal doubled frequency circulating current and the optimal bias voltage.

8. An electronic device, characterized in that: The electronic device includes a memory and a processor, wherein a computer program is stored in the memory. When the computer program is executed by the processor, the processor performs the steps of the harmonic optimization method based on double frequency circulating current injection as described in any one of claims 1 to 6.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed, the steps of the harmonic optimization method based on double frequency circulating current injection as described in any one of claims 1 to 6 are implemented.

10. A computer program product, characterized in that The computer program product includes a computer program stored on a non-transitory computer-readable storage medium, wherein the computer program includes program instructions, wherein when the program instructions are executed by a computer, the computer is caused to perform the steps of the harmonic optimization method based on double frequency circulating current injection as described in any one of claims 1 to 6.

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