Grid-forming high-voltage direct-hanging energy storage system and control method thereof

Abstract

The application provides a grid-connected high-voltage direct-hanging energy storage system and a control method thereof, comprising a modular multilevel converter in which a plurality of sub-modules are arranged, each of the sub-modules is further provided with a semiconductor switch, a high-voltage direct-current capacitor, a DC / DC buffer module and an energy storage battery, the semiconductor switch and the high-voltage direct-current capacitor form a half-bridge type topology, and the energy storage battery is connected with the half-bridge type topology through the DC / DC buffer module; a grid power control module, a circulating current harmonic control module and a battery SOC equalization control module are in communication connection with the modular multilevel converter; the grid power control module is used for adjusting the output voltage of the modular multilevel converter; the circulating current harmonic control module is used for adjusting the harmonic component of the modular multilevel converter; and the battery SOC equalization control module is used for adjusting the battery balance of the modular multilevel converter. Through grid control, each sub-module is accurately controlled, and the active power and the reactive power of the energy storage system are quickly and accurately adjusted.

Description

Technical Field

[0001] This invention relates to the field of energy storage systems, specifically to a grid-connected high-voltage direct-connected energy storage system and its control method. Background Technology

[0002] With the rapid increase in renewable energy penetration and the surge in demand for flexible power system resources, large-scale energy storage power stations have become a key support for building new power systems. Traditional low-voltage energy storage connects to the grid through multi-stage DC / AC conversion and step-up transformers, which suffers from problems such as large equipment size, significant efficiency loss, and limited harmonic suppression capabilities. To address these issues, high-voltage direct-connection energy storage technology, which connects energy storage units in series to achieve direct high-voltage grid connection, eliminates the need for a separate transformer and demonstrates significant advantages in reducing system losses and increasing power density.

[0003] Existing high-voltage direct-connected energy storage systems mostly employ chained H-bridges or cascaded two-level topologies. While these partially solve the voltage adaptation problem, they still have significant shortcomings in terms of dynamic response speed, modular scalability, and fault ride-through reliability. Especially when applied to grid-forming scenarios, existing solutions struggle to simultaneously address virtual inertia support, wideband impedance characteristic adjustment, and coordinated control among multiple modules. For example, traditional voltage equalization strategies are prone to causing SOC imbalances among submodules during power surges, limiting system output capability; and insufficient coupling between grid-forming control algorithms and modular hardware architecture leads to a decrease in system stability margin under dynamic operating conditions.

[0004] In recent years, modular multilevel transformers (MMCs) have been widely used in high-voltage direct current (HVDC) transmission due to their high modularity, excellent output waveform quality, and strong fault tolerance. However, directly transplanting MMC topology to the energy storage field faces two major technical bottlenecks: First, the energy interaction between energy storage units and power modules requires the reconstruction of the capacitor voltage control logic of traditional MMCs, and existing energy management strategies based on fixed modulation ratios are difficult to adapt to the dynamic changes in the SOC of energy storage systems; Second, the contradiction between the strong grid construction capability required for grid-based control and the multivariable coupling characteristics of MMCs has not been effectively resolved, especially in weak grid / island conditions where subsynchronous oscillations are easily triggered. Summary of the Invention

[0005] Based on this, the present invention provides a grid-type high-voltage direct-connected energy storage system and its control method. Through hardware topology innovation and control strategy collaborative design, it breaks through the limitations of existing technologies in terms of high dynamic response, multi-objective optimization control and system-level stability improvement.

[0006] In a first aspect, the present invention provides a grid-type high-voltage direct-connected energy storage system, the grid-type high-voltage direct-connected energy storage system comprising a modular multilevel converter, a grid power control module, a circulating harmonic control module, and a battery SOC equalization control module;

[0007] The modular multilevel converter is provided with several sub-modules. Each sub-module is also provided with a semiconductor switch, a high-voltage DC capacitor, a DC / DC buffer module and an energy storage battery. The semiconductor switch and the high-voltage DC capacitor form a half-bridge topology. The energy storage battery is connected to the half-bridge topology through the DC / DC buffer module.

[0008] The grid power control module, circulating harmonic control module, and battery SOC equalization control module are communicatively connected to the modular multilevel converter.

[0009] The grid power control module is used to adjust the output voltage of the modular multilevel converter.

[0010] The circulating harmonic control module is used to adjust the harmonic components of the modular multilevel converter.

[0011] The battery SOC balancing control module is used to adjust the battery balance of the modular multilevel converter.

[0012] Furthermore, the sub-modules contained in each arm of the modular multilevel converter constitute an equivalent average value model;

[0013] The specific expression for the equivalent average model is:

[0014] ,

[0015] in, For the AC terminal voltage of the modular multilevel converter, For bridge arm inductance, For the bridge arm resistance, for Phase upper arm current, for Lower bridge arm current, for Phase upper arm voltage, for Lower bridge arm voltage, DC voltage for Phase upper arm modulation ratio, for Down-phase bridge arm modulation ratio, This is the rated voltage on the DC side. For the base frequency The amplitude of the modulation ratio, For the base frequency The phase angle of the modulation ratio, The amplitude of the frequency doubling modulation ratio. The phase angle is the frequency multiplication ratio. The equivalent capacitance of the bridge arm. for Mutually The voltage of the submodule capacitor in the bridge arm. for Mutually Bridge arm modulation ratio, for Mutually The submodule output current of the bridge arm, The duty cycle of the DC / DC module. For the number of bridge arm sub-modules, For the energy storage battery branch inductor, For energy storage battery current, This refers to the voltage of the energy storage battery.

[0016] Furthermore, the grid power control module is used to adjust the output voltage of the modular multilevel converter, specifically expressed as follows:

[0017]

[0018]

[0019]

[0020]

[0021]

[0022]

[0023]

[0024] in, The inertia coefficient, The active damping coefficient is... The system angular frequency, The system's rated angular frequency, To output active power to the converter, This is the setpoint for the converter's output active power. To control the output voltage reference value, This is the converter output voltage. This is the given value for the converter output voltage. This is the reactive damping coefficient. Here, is the reactive power integral coefficient, and s is the differential sign in the frequency domain. This is the given value for the reactive power output of the converter. To output reactive power to the converter, This refers to the proportional gain coefficient of the voltage outer loop controller. This represents the integral gain coefficient of the voltage outer loop controller. The first voltage reference value obtained from reactive power-voltage control. The second voltage reference value is obtained from reactive power-voltage control. This is the first output command value of the outer voltage loop. This is the second output command value of the outer voltage loop. This refers to the proportional gain coefficient of the voltage inner loop controller. This represents the integral gain coefficient of the voltage inner loop controller. This is the first output voltage reference value generated by the current inner loop control. This is the second output voltage reference value generated by the voltage inner loop control. For converter to control grid voltage Axial components, For converter to control grid voltage Axial components, Injecting grid current into the converter Axial components, Injecting grid current into the converter Axial components.

[0025] Furthermore, the circulating harmonic control module is used to adjust the harmonic components of the modular multilevel converter, and the specific expression is as follows:

[0026]

[0027]

[0028] in, for Internal circulating current of modular multilevel converter For modular multilevel converters Phase upper arm current, For modular multilevel converters Lower bridge arm current, PR controls the proportional gain coefficient. The integral gain coefficient for PC control. This is the transfer function of a bandpass filter, used to obtain the harmonics in the circulating current.

[0029] Furthermore, the battery SOC balancing control module is used to adjust the battery balance of the modular multilevel converter, and the specific expression is as follows:

[0030]

[0031]

[0032]

[0033]

[0034]

[0035]

[0036]

[0037] in, for The total SOC of the battery phases, for The sum of the SOC of the upper bridge arm. for The sum of the SOC of the lower bridge arm, for Real-time average SOC of the upper and lower bridge arms for Mutually Real-time average SOC of the bridge arm This represents the real-time average SOC of each phase of the modular multilevel converter. For modular multilevel converters Real-time average value of phase SOC For modular multilevel converters Real-time average value of phase SOC For modular multilevel converters Real-time average value of phase SOC For the revised version Phase SOC power, The SOC equalization factor for each phase of the modular multilevel converter. The bridge arm SOC balance coefficient, for Mutually Corrected power of bridge arm battery energy storage for Mutually The rated output current of the bridge arm battery energy storage. for Mutually Real-time output power of the bridge arm battery energy storage, for Mutually Duty cycle of the DC / DC link for battery energy storage in the bridge arm. for Mutually Real-time output current of the bridge arm battery energy storage, The proportional gain of the outer loop PI element in the power circuit. The integral coefficient of the PI element in the power outer loop is denoted as . This is the proportional coefficient of the PI element in the inner current loop. is the integral coefficient of the PI element in the inner current loop.

[0038] In a second aspect, the present invention also provides a control method for a grid-type high-voltage direct-connected energy storage system, wherein the grid-type high-voltage direct-connected energy storage system described in any one of the first aspects is directly connected to a high-voltage power grid, and the grid-type high-voltage direct-connected energy storage system is externally connected to an LCC high-voltage DC transmission system.

[0039] The output voltage of the modular multilevel converter is adjusted by the grid power control module to stabilize the output voltage of the modular multilevel converter.

[0040] The harmonic components of the modular multilevel converter are adjusted by the circulating harmonic control module to reduce the losses caused by the circulating current in the grid-connected energy storage system.

[0041] The battery balance of the modular multilevel converter is adjusted by the battery SOC equalization control module.

[0042] Furthermore, the specific expression for adjusting the output voltage of the modular multilevel converter through the grid power control module to stabilize the output voltage of the modular multilevel converter is as follows:

[0043]

[0044]

[0045]

[0046]

[0047]

[0048]

[0049]

[0050] in, The inertia coefficient, The active damping coefficient is... The system angular frequency, The system's rated angular frequency, To output active power to the converter, This is the setpoint for the converter's output active power. To control the output voltage reference value, This is the converter output voltage. This is the given value for the converter output voltage. This is the reactive damping coefficient. Here, is the reactive power integral coefficient, and s is the differential sign in the frequency domain. This is the given value for the reactive power output of the converter. To output reactive power to the converter, This refers to the proportional gain coefficient of the voltage outer loop controller. This represents the integral gain coefficient of the voltage outer loop controller. The first voltage reference value obtained from reactive power-voltage control. The second voltage reference value is obtained from reactive power-voltage control. This is the first output command value of the outer voltage loop. This is the second output command value of the outer voltage loop. This refers to the proportional gain coefficient of the voltage inner loop controller. This represents the integral gain coefficient of the voltage inner loop controller. This is the first output voltage reference value generated by the current inner loop control. This is the second output voltage reference value generated by the voltage inner loop control. For converter to control grid voltage Axial components, For converter to control grid voltage Axial components, Injecting grid current into the converter Axial components, Injecting grid current into the converter Axial components.

[0051] Furthermore, the harmonic components of the modular multilevel converter are adjusted by the circulating harmonic control module to reduce the losses caused by the circulating current in the grid-connected energy storage system. The specific expression is as follows:

[0052]

[0053]

[0054] in, for Internal circulating current of modular multilevel converter For modular multilevel converters Phase upper arm current, For modular multilevel converters Lower bridge arm current, PR controls the proportional gain coefficient. The integral gain coefficient for PC control. This is the transfer function of a bandpass filter, used to obtain the harmonics in the circulating current.

[0055] Furthermore, the specific expression for adjusting the battery balance of the modular multilevel converter through the battery SOC balancing control module is as follows:

[0056]

[0057]

[0058]

[0059]

[0060]

[0061]

[0062]

[0063] in, for The total SOC of the battery phases, for The sum of the SOC of the upper bridge arm. for The sum of the SOC of the lower bridge arm, for Real-time average SOC of the upper and lower bridge arms for Mutually Real-time average SOC of the bridge arm This represents the real-time average SOC of each phase of the modular multilevel converter. For modular multilevel converters Real-time average value of phase SOC For modular multilevel converters Real-time average value of phase SOC For modular multilevel converters Real-time average value of phase SOC For the revised version Phase SOC power, The SOC equalization factor for each phase of the modular multilevel converter. The bridge arm SOC balance coefficient, for Mutually Corrected power of bridge arm battery energy storage for Mutually The rated output current of the bridge arm battery energy storage. for Mutually Real-time output power of the bridge arm battery energy storage, for Mutually Duty cycle of the DC / DC link for battery energy storage in the bridge arm. for Mutually Real-time output current of the bridge arm battery energy storage, The proportional gain of the outer loop PI element in the power circuit. The integral coefficient of the PI element in the power outer loop is denoted as . This is the proportional coefficient of the PI element in the inner current loop. is the integral coefficient of the PI element in the inner current loop.

[0064] Thirdly, the present invention also provides a computer-readable storage medium having a computer program stored thereon, wherein the computer program, when executed by a processor, implements the steps of the control method for the grid-type high-voltage direct-connected energy storage system as described in any of the second aspects.

[0065] Fourthly, the present invention also provides a computer device, including a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, it executes the control method of the grid-type high-voltage direct-connected energy storage system according to any one of the second aspects.

[0066] The beneficial effects of adopting the above technical solution are as follows: This embodiment constructs a high-voltage direct-connected energy storage model by establishing a modular multilevel converter under grid control and realizing the SOC balancing of its internal energy storage batteries, providing a model reference for the analysis of current grid-connected high-voltage direct-connected energy storage access to power systems. Furthermore, for the case where energy storage batteries are connected to sub-modules via DC / DC buffer modules, a sub-module average value model is established. The numerous sub-modules on a single bridge arm are equated to a single sub-module, simplifying the high-voltage direct-connected energy storage model and avoiding the problem of excessive sub-modules and complex models in MMC. Even further, grid control allows for precise control of each sub-module, enabling rapid and accurate adjustment of the active and reactive power of the energy storage system. It can accurately output or absorb specific amounts of power according to the actual needs of the grid, better meeting the grid's regulation requirements. Furthermore, PR harmonic control is used to control the main harmonic components in the circulating current, suppressing them as much as possible, avoiding additional losses and equipment heating caused by the circulating current, and improving the system's operating efficiency and reliability. Furthermore, by adjusting the reference power of the energy storage battery through real-time SOC changes of each module, the SOC state of each battery is balanced, improving charging and discharging efficiency and enhancing the overall output stability of the battery pack. Attached Figure Description

[0067] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0068] Figure 1 This is a topology diagram of a modular multilevel converter in a grid-connected high-voltage direct-connected energy storage system according to one embodiment of this application;

[0069] Figure 2 This is a schematic diagram of a control method for a grid-type high-voltage direct-connected energy storage system in one embodiment of this application;

[0070] Figure 3 This is a schematic diagram illustrating the control principle of a grid-type high-voltage direct-connected energy storage system in one embodiment of this application;

[0071] Figure 4 This is a schematic diagram illustrating the verification of the SOC equalization control effect in one embodiment of this application;

[0072] Figure 5 This is a schematic diagram of the three-phase upper arm capacitor voltage curve in one embodiment of this application;

[0073] Figure 6 This is a schematic diagram of the three-phase internal circulation curve in one embodiment of this application;

[0074] Figure 7 This is a schematic diagram of the power curve under fault ride-through of the LCC sending-end system in one embodiment of this application. Detailed Implementation

[0075] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. To describe the present invention in more detail, the grid-type high-voltage direct-connected energy storage system and its control method provided by the present invention will be specifically described below with reference to the accompanying drawings.

[0076] Unless otherwise defined, the technical or scientific terms used in this application shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Similarly, the terms "an," "a," or "the" do not indicate a quantity limitation, but rather indicate the presence of at least one. The terms "comprising" or "including" mean that the preceding element or object encompasses the elements or objects listed after the word and their equivalents, without excluding other elements or objects. The terms "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. "Up," "down," "left," "right," etc., are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0077] Combined with appendix Figure 1 The diagram shows a topology of a modular multilevel converter in a grid-connected high-voltage energy storage system. This application provides a grid-connected high-voltage direct-connected energy storage system, which includes a modular multilevel converter, a grid power control module, a circulating harmonic control module, and a battery SOC equalization control module.

[0078] The modular multilevel converter is provided with several sub-modules. Each sub-module is also provided with a semiconductor switch, a high-voltage DC capacitor, a DC / DC buffer module and an energy storage battery. The semiconductor switch and the high-voltage DC capacitor form a half-bridge topology. The energy storage battery is connected to the half-bridge topology through the DC / DC buffer module.

[0079] The grid power control module, circulating harmonic control module, and battery SOC equalization control module are communicatively connected to the modular multilevel converter.

[0080] The grid power control module is used to adjust the output voltage of the modular multilevel converter.

[0081] The circulating harmonic control module is used to adjust the harmonic components of the modular multilevel converter.

[0082] The battery SOC balancing control module is used to adjust the battery balance of the modular multilevel converter.

[0083] In this modular multilevel converter, each bridge arm contains sub-modules that constitute an equivalent average value model;

[0084] The specific expression for the equivalent average model is:

[0085] ,

[0086] in, For the AC terminal voltage of the modular multilevel converter, For bridge arm inductance, For the bridge arm resistance, for Phase upper arm current, for Lower bridge arm current, for Phase upper arm voltage, for Lower bridge arm voltage, DC voltage for Phase upper arm modulation ratio, for Down-phase bridge arm modulation ratio, This is the rated voltage on the DC side. For the base frequency The amplitude of the modulation ratio, For the base frequency The phase angle of the modulation ratio, The amplitude of the frequency doubling modulation ratio. The phase angle is the frequency multiplication ratio. The equivalent capacitance of the bridge arm. for Mutually The voltage of the submodule capacitor in the bridge arm. for Mutually Bridge arm modulation ratio, for Mutually The submodule output current of the bridge arm, The duty cycle of the DC / DC module. For the number of bridge arm sub-modules, For the energy storage battery branch inductor, For energy storage battery current, This refers to the voltage of the energy storage battery.

[0087] By establishing an average value model, the energy storage battery is introduced into the capacitor section of the submodule in the form of a controlled current source. The DC / DC module is equivalent to a controlled voltage source from the perspective of the energy storage battery. From the perspective of the modular multilevel converter, the submodule is equivalent to a controlled voltage source, thus establishing an equivalent average value model.

[0088] Based on the above topology, the grid power control module provides inertial support for the system. This is manifested in the grid power control module's adjustment of the output voltage of the modular multilevel converter, specifically expressed as follows:

[0089]

[0090]

[0091]

[0092]

[0093]

[0094]

[0095]

[0096] in, The inertia coefficient, The active damping coefficient is... The system angular frequency, The system's rated angular frequency, To output active power to the converter, This is the setpoint for the converter's output active power. To control the output voltage reference value, This is the converter output voltage. This is the given value for the converter output voltage. This is the reactive damping coefficient. Here, is the reactive power integral coefficient, and s is the differential sign in the frequency domain. This is the given value for the reactive power output of the converter. To output reactive power to the converter, This refers to the proportional gain coefficient of the voltage outer loop controller. This represents the integral gain coefficient of the voltage outer loop controller. The first voltage reference value obtained from reactive power-voltage control. The second voltage reference value is obtained from reactive power-voltage control. This is the first output command value of the outer voltage loop. This is the second output command value of the outer voltage loop. This refers to the proportional gain coefficient of the voltage inner loop controller. This represents the integral gain coefficient of the voltage inner loop controller. This is the first output voltage reference value generated by the current inner loop control. This is the second output voltage reference value generated by the voltage inner loop control. For converter to control grid voltage Axial components, For converter to control grid voltage Axial components, Injecting grid current into the converter Axial components, Injecting grid current into the converter Axial components.

[0097] It should be noted that in this embodiment, the grid power control module can be configured using a virtual synchronous machine. After the active power-frequency and reactive power-voltage control modules of the grid power control module are implemented, a dual-loop voltage and current control is applied to stabilize the output voltage. Simultaneously, direct modulation is employed, using the sum of the rated capacitor voltages as the divisor.

[0098] Meanwhile, under direct modulation, the steady-state arm current contains a circulating current dominated by the second harmonic, which needs to be suppressed. Therefore, the circulating harmonic control module is used to adjust the harmonic components of the modular multilevel converter, that is, to suppress the harmonic components of the second harmonic in the system. The specific expression is as follows:

[0099]

[0100]

[0101] in, for Internal circulating current of modular multilevel converter For modular multilevel converters Phase upper arm current, For modular multilevel converters Lower bridge arm current, PR controls the proportional gain coefficient. The integral gain coefficient for PC control. This is the transfer function of a bandpass filter, used to obtain the harmonics in the circulating current.

[0102] The above-mentioned circulating harmonic control module controls the frequency doubling circulating current, keeping it as close to zero as possible through PR control, thereby reducing the losses caused by the circulating current within the system.

[0103] Furthermore, imbalance of the state of charge (SOC) within energy storage batteries is one of the main causes of power station accidents, especially in high-voltage direct-connected energy storage systems with a large number of battery models. It is necessary to monitor the SOC of each battery and implement balancing control strategies to ensure battery safety and maximum energy utilization. This embodiment employs intra-phase and arm SOC balancing control, specifically, the battery SOC balancing control module is used to adjust the battery balance of the modular multilevel converter. The expression is:

[0104]

[0105]

[0106]

[0107]

[0108]

[0109]

[0110]

[0111] in, for The total SOC of the battery phases, for The sum of the SOC of the upper bridge arm. for The sum of the SOC of the lower bridge arm, for Real-time average SOC of the upper and lower bridge arms for Mutually Real-time average SOC of the bridge arm This represents the real-time average SOC of each phase of the modular multilevel converter. For modular multilevel converters Real-time average value of phase SOC For modular multilevel converters Real-time average value of phase SOC For modular multilevel converters Real-time average value of phase SOC For the revised version Phase SOC power, The SOC equalization factor for each phase of the modular multilevel converter. The bridge arm SOC balance coefficient, for Mutually Corrected power of bridge arm battery energy storage for Mutually The rated output current of the bridge arm battery energy storage. for Mutually Real-time output power of the bridge arm battery energy storage, for Mutually Duty cycle of the DC / DC link for battery energy storage in the bridge arm. for Mutually Real-time output current of the bridge arm battery energy storage, The proportional gain of the outer loop PI element in the power circuit. The integral coefficient of the PI element in the power outer loop is denoted as . This is the proportional coefficient of the PI element in the inner current loop. is the integral coefficient of the PI element in the inner current loop.

[0112] Based on the above-mentioned grid-connected high-voltage direct-connection energy storage system, combined with the attached Figure 2 The schematic diagram and appendix show the control method of the grid-type high-voltage direct-connected energy storage system. Figure 3 The schematic diagram shown illustrates the control method principle of a grid-connected high-voltage direct-connected energy storage system. This embodiment also provides a control method for a grid-connected high-voltage direct-connected energy storage system, which directly connects the aforementioned grid-connected high-voltage direct-connected energy storage system to a high-voltage power grid, while simultaneously connecting the grid-connected high-voltage direct-connected energy storage system to an external LCC high-voltage DC transmission system. The specific control method includes the following steps:

[0113] Step S1: Adjust the output voltage of the modular multilevel converter through the grid power control module to stabilize the output voltage of the modular multilevel converter.

[0114] The specific expression for adjusting the output voltage of the modular multilevel converter through the grid power control module to stabilize the output voltage of the modular multilevel converter is as follows:

[0115]

[0116]

[0117]

[0118]

[0119]

[0120]

[0121]

[0122] in, The inertia coefficient, The active damping coefficient is... The system angular frequency, The system's rated angular frequency, To output active power to the converter, This is the setpoint for the converter's output active power. To control the output voltage reference value, This is the converter output voltage. This is the given value for the converter output voltage. This is the reactive damping coefficient. Here, is the reactive power integral coefficient, and s is the differential sign in the frequency domain. This is the given value for the reactive power output of the converter. To output reactive power to the converter, This refers to the proportional gain coefficient of the voltage outer loop controller. This represents the integral gain coefficient of the voltage outer loop controller. The first voltage reference value obtained from reactive power-voltage control. The second voltage reference value is obtained from reactive power-voltage control. This is the first output command value of the outer voltage loop. This is the second output command value of the outer voltage loop. This refers to the proportional gain coefficient of the voltage inner loop controller. This represents the integral gain coefficient of the voltage inner loop controller. This is the first output voltage reference value generated by the current inner loop control. This is the second output voltage reference value generated by the voltage inner loop control. For converter to control grid voltage Axial components, For converter to control grid voltage Axial components, Injecting grid current into the converter Axial components, Injecting grid current into the converter Axial components.

[0123] After the active-frequency and reactive-voltage control modules of the grid power control module are applied, a dual-loop voltage and current control is connected to stabilize the output voltage. Simultaneously, direct modulation is employed, using the sum of the rated capacitor voltages as the divisor.

[0124] Step S2: Adjust the harmonic components of the modular multilevel converter through the circulating harmonic control module to reduce the losses caused by the circulating current in the grid-connected energy storage system.

[0125] In the case of direct modulation, the steady-state arm current contains a circulating current dominated by the second harmonic, which needs to be suppressed through alignment. The circulating current harmonic control module adjusts the harmonic components of the modular multilevel converter to reduce the losses caused by the circulating current in the grid-type direct-connected energy storage system. The specific expression is as follows:

[0126]

[0127]

[0128] in, for Internal circulating current of modular multilevel converter For modular multilevel converters Phase upper arm current, For modular multilevel converters Lower bridge arm current, PR controls the proportional gain coefficient. The integral gain coefficient for PC control. This is the transfer function of a bandpass filter, used to obtain the harmonics in the circulating current.

[0129] This is used to control the frequency doubling circulating current, keeping it as close to zero as possible through PR control, thereby reducing the losses caused by the circulating current within the system.

[0130] Step S3: Adjust the battery balance of the modular multilevel converter through the battery SOC equalization control module.

[0131] The specific expression for adjusting the battery balance of the modular multilevel converter through the battery SOC balancing control module is as follows:

[0132]

[0133]

[0134]

[0135]

[0136]

[0137]

[0138]

[0139] in, for The total SOC of the battery phases, for The sum of the SOC of the upper bridge arm. for The sum of the SOC of the lower bridge arm, for Real-time average SOC of the upper and lower bridge arms for Mutually Real-time average SOC of the bridge arm This represents the real-time average SOC of each phase of the modular multilevel converter. For modular multilevel converters Real-time average value of phase SOC For modular multilevel converters Real-time average value of phase SOC For modular multilevel converters Real-time average value of phase SOC For the revised version Phase SOC power, The SOC equalization factor for each phase of the modular multilevel converter. The bridge arm SOC balance coefficient, for Mutually Corrected power of bridge arm battery energy storage for Mutually The rated output current of the bridge arm battery energy storage. for Mutually Real-time output power of the bridge arm battery energy storage, for Mutually Duty cycle of the DC / DC link for battery energy storage in the bridge arm. for Mutually Real-time output current of the bridge arm battery energy storage, The proportional gain of the outer loop PI element in the power circuit. The integral coefficient of the PI element in the power outer loop is denoted as . This is the proportional coefficient of the PI element in the inner current loop. is the integral coefficient of the PI element in the inner current loop.

[0140] To better illustrate the supporting role of the control method of the grid-connected high-voltage direct-connected energy storage system in this embodiment, an example is taken where the high-voltage direct-connected energy storage is directly connected to a 550kV high-voltage grid, the energy storage capacitor is set to 500MW, and an external LCC high-voltage DC transmission system is connected. First, the initial SOC of the battery storage modules within the modular multilevel converter is set to be different to verify its SOC balancing performance; then, a fault is set to illustrate the supporting role of the grid-connected high-voltage direct-connected energy storage system on the power grid.

[0141] Because an average value model is used for modeling, submodules on a single bridge arm are equivalently merged into one submodule, thus eliminating the need for intra-module equalization. The SOC equalization employed in this invention primarily involves real-time monitoring of the SOC value of each module and adjusting the specified power value of the battery modules based on the SOC differences between the three phases and between the upper and lower bridge arms within each phase. PI control is then used to track the battery output power to the specified value, ensuring that batteries with higher SOC output more power and batteries with lower SOC output less power, thereby guaranteeing energy balance in the energy storage batteries. , The two SOC equalization coefficients determine the SOC equalization rate of the energy storage battery. , The larger the value, the faster the equalization rate, but excessively large values... , This could lead to excessively large inputs for instantaneous PI control, causing system instability, and therefore requires careful consideration. , Size.

[0142] set up , , , , , This allows for the verification of the SOC equalization control strategy in this embodiment. The results are as follows... Figure 4 As shown, when the initial SOC of each module is different, under SOC balancing control, the SOC of each module gradually tends to balance over time, and after 30 seconds, the SOC can be considered to be the same, thus achieving the purpose of SOC balancing. Simultaneously, during this process, the capacitor voltages of each module tend to be the same, as... Figure 5 As shown, the capacitor voltage values ​​of the three-phase upper bridge arm modules (abc) tend to balance, proving that the SOC balancing control can also achieve voltage balancing, making the capacitor voltages of each module the same. Furthermore, Figure 6 The diagram shown is a simulation of the three-phase circulating current in the bridge arm. It can be seen that the three-phase circulating currents are also relatively balanced. Furthermore, due to the adoption of the circulating current harmonic suppression control strategy, there is basically no second harmonic component in the internal circulating current, resulting in high current quality.

[0143] In this embodiment, high-voltage direct-connected energy storage replaces conventional energy storage at the LCC DC transmission terminal. A single-phase ground fault is set at the PCC at 10 seconds, and the fault is cleared at 10.1 seconds. The system power response curve is as follows. Figure 7 As shown in the diagram, during the fault, the LCC (Limited Current Control) cuts off current, resulting in no power flow. At this time, power reverses through the grid, and the high-voltage direct-connected energy storage improves power output and stabilizes the system. After the fault is cleared, the LCC current-cutting phenomenon disappears, the entire system stabilizes, and fault ride-through is completed.

[0144] It should be understood that, although attached Figure 2 The steps in the flowchart are shown sequentially according to the arrows, but these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified in this document, there is no strict order requirement for the execution of these steps, and they can be executed in other orders. Furthermore, [the following is a list of steps]. Figure 2 At least some of the steps in the process may include multiple sub-steps or sub-stages. These sub-steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these sub-steps or stages is not necessarily sequential, but can be executed in turn or alternately with other steps or at least some of the sub-steps or stages of other steps.

[0145] In one embodiment, the present invention also provides a computer-readable storage medium having a computer program stored thereon, wherein the computer program, when executed by a processor, implements the steps of the control method for the grid-type high-voltage direct-connected energy storage system described above.

[0146] The computer-readable storage medium may be an electronic storage device such as flash memory, EEPROM (Electrically Erasable Programmable Read-Only Memory), EPROM (Erasable Programmable Read-Only Memory), hard disk, or ROM. Optionally, the computer-readable storage medium includes a non-transitory computer-readable storage medium. The computer-readable storage medium has storage space for program code that performs any of the method steps described above. This program code can be read from or written to one or more computer program products, and the program code may be compressed in an appropriate form.

[0147] In one embodiment, the present invention provides a computer device including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to perform the control method of the above-described grid-type high-voltage direct-connected energy storage system.

[0148] The computer device includes a memory, a processor, and one or more computer programs, wherein the one or more computer programs can be stored in the memory and configured to be executed by one or more processors, and the one or more application programs are configured to execute the control method of the above-described grid-type high-voltage direct-connected energy storage system.

[0149] A processor may include one or more processing cores. The processor connects to various parts of the computer device using various interfaces and lines, and performs various functions and processes data by running or executing instructions, programs, code sets, or instruction sets stored in memory, and by calling data stored in memory. Optionally, the processor may be implemented using at least one hardware form of Digital Signal Processing (DSP), Field-Programmable Gate Array (FPGA), or Programmable Logic Array (PLA). The processor may integrate one or a combination of several of the following: Central Processing Unit (CPU), Graphics Processing Unit (GPU), and modem. The CPU primarily handles the operating system, user interface, and applications; the GPU is responsible for rendering and drawing the displayed content; and the modem handles wireless communication. It is understood that the modem may also be implemented separately as a communication chip, without being integrated into the processor.

[0150] The memory may include random access memory (RAM) or read-only memory (ROM). The memory can be used to store instructions, programs, code, code sets, or instruction sets. The memory may include a program storage area and a data storage area. The program storage area may store instructions for implementing an operating system, instructions for implementing at least one function (such as touch functionality, sound playback functionality, image playback functionality, etc.), and instructions for implementing the various method embodiments described above. The data storage area may also store data created by the terminal device during use.

[0151] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A grid-connected high-voltage direct-connection energy storage system, characterized in that, The grid-type high-voltage direct-connected energy storage system includes a modular multilevel converter, a grid power control module, a circulating harmonic control module, and a battery SOC equalization control module. The modular multilevel converter is equipped with several sub-modules. Each sub-module is equipped with a semiconductor switch, a high-voltage DC capacitor, a DC / DC buffer module, and an energy storage battery. Semiconductor switches T1 and T2 and the high-voltage DC capacitor form a first half-bridge topology, and semiconductor switches T3 and T4 form a second half-bridge topology. The energy storage battery is connected in series with the DC / DC buffer module and then connected across the two ends of semiconductor switch T4. The second half-bridge topology is connected in parallel with the high-voltage DC capacitor. The grid power control module, circulating harmonic control module, and battery SOC equalization control module are communicatively connected to the modular multilevel converter. The grid power control module is used to adjust the output voltage of the modular multilevel converter. The circulating harmonic control module is used to adjust the harmonic components of the modular multilevel converter. The battery SOC equalization control module is used to adjust the battery balance of the modular multilevel converter. The sub-modules contained in each arm of the modular multilevel converter constitute an equivalent average value model. The specific expression for the equivalent average model is: ， in, For the AC terminal voltage of the modular multilevel converter, For bridge arm inductance, For the bridge arm resistance, for Phase upper arm current, for Lower bridge arm current, for Phase upper arm voltage, for Lower bridge arm voltage, DC voltage for Phase upper arm modulation ratio, for Down-phase bridge arm modulation ratio, For the base frequency The amplitude of the modulation ratio, For the base frequency The phase angle of the modulation ratio, The amplitude of the frequency doubling modulation ratio. The phase angle is the frequency multiplication ratio. The equivalent capacitance of the bridge arm. for Mutually The voltage of the submodule capacitor in the bridge arm. for Mutually Bridge arm modulation ratio, for Mutually The submodule output current of the bridge arm, The duty cycle of the DC / DC module. For the number of bridge arm sub-modules, For the energy storage battery branch inductor, For energy storage battery current, This refers to the voltage of the energy storage battery. The grid power control module is used to adjust the output voltage of the modular multilevel converter, and the specific expression is as follows: ； ； ； ； ； ； ； in, The inertia coefficient, The active damping coefficient is... The system angular frequency, The system's rated angular frequency, To output active power to the converter, This is the setpoint for the converter's output active power. To control the output voltage reference value, This is the converter output voltage. This is the given value for the converter output voltage. This is the reactive damping coefficient. Here, is the reactive power integral coefficient, and s is the differential sign in the frequency domain. This is the given value for the reactive power output of the converter. To output reactive power to the converter, This refers to the proportional gain coefficient of the voltage outer loop controller. This represents the integral gain coefficient of the voltage outer loop controller. The first voltage reference value obtained from reactive power-voltage control. The second voltage reference value is obtained from reactive power-voltage control. This is the first output command value of the outer voltage loop. This is the second output command value of the outer voltage loop. This refers to the proportional gain coefficient of the voltage inner loop controller. This represents the integral gain coefficient of the voltage inner loop controller. This is the first output voltage reference value generated by the current inner loop control. This is the second output voltage reference value generated by the voltage inner loop control. For converter to control grid voltage Axial components, For converter to control grid voltage Axial components, Injecting grid current into the converter Axial components, Injecting grid current into the converter Axial components.

2. The grid-type high-voltage direct-connected energy storage system as described in claim 1, characterized in that, The circulating harmonic control module is used to adjust the harmonic components of the modular multilevel converter, and the specific expression is as follows: ； ； in, for Internal circulating current of modular multilevel converter For modular multilevel converters Phase upper arm current, For modular multilevel converters Lower bridge arm current, PR controls the proportional gain coefficient. The integral gain coefficient for PC control. This is the transfer function of a bandpass filter, used to obtain the harmonics in the circulating current.

3. The grid-type high-voltage direct-connected energy storage system as described in claim 2, characterized in that, The battery SOC balancing control module is used to adjust the battery balance of the modular multilevel converter, and the specific expression is as follows: ； ； ； ； ； ； ； in, for The total SOC of the battery phases, for The sum of the SOC of the upper bridge arm. for The sum of the SOC of the lower bridge arm, for Real-time average SOC of the upper and lower bridge arms for Mutually Real-time average SOC of the bridge arm This represents the real-time average SOC of each phase of the modular multilevel converter. For modular multilevel converters Real-time average value of phase SOC For modular multilevel converters Real-time average value of phase SOC For modular multilevel converters Real-time average value of phase SOC For the revised version Phase SOC power, The SOC equalization factor for each phase of the modular multilevel converter. The bridge arm SOC balance coefficient, for Mutually Corrected power of bridge arm battery energy storage for Mutually The rated output current of the bridge arm battery energy storage. for Mutually Real-time output power of the bridge arm battery energy storage, for Mutually Duty cycle of the DC / DC link for battery energy storage in the bridge arm. for Mutually Real-time output current of the bridge arm battery energy storage, The proportional gain of the outer loop PI element in the power circuit. The integral coefficient of the PI element in the power outer loop is denoted as . This is the proportional coefficient of the PI element in the inner current loop. is the integral coefficient of the PI element in the inner current loop.

4. A control method for a grid-connected high-voltage direct-connected energy storage system, characterized in that, The grid-type high-voltage direct-connected energy storage system as described in any one of claims 1-3 is directly connected to the high-voltage power grid, and the grid-type high-voltage direct-connected energy storage system is externally connected to an LCC high-voltage DC transmission system. The output voltage of the modular multilevel converter is adjusted by the grid power control module to stabilize the output voltage of the modular multilevel converter. The harmonic components of the modular multilevel converter are adjusted by the circulating harmonic control module to reduce the losses caused by the circulating current in the grid-connected energy storage system. The battery balance of the modular multilevel converter is adjusted by the battery SOC equalization control module.

5. The control method for a grid-type high-voltage direct-connected energy storage system as described in claim 4, characterized in that, The process of adjusting the output voltage of the modular multilevel converter through the grid power control module to stabilize the output voltage of the modular multilevel converter is specifically expressed as follows: ； ； ； ； ； ； ； in, The inertia coefficient, The active damping coefficient is... The system angular frequency, The system's rated angular frequency, To output active power to the converter, This is the setpoint for the converter's output active power. To control the output voltage reference value, This is the converter output voltage. This is the given value for the converter output voltage. This is the reactive damping coefficient. Here, is the reactive power integral coefficient, and s is the differential sign in the frequency domain. This is the given value for the reactive power output of the converter. To output reactive power to the converter, This refers to the proportional gain coefficient of the voltage outer loop controller. This represents the integral gain coefficient of the voltage outer loop controller. The first voltage reference value obtained from reactive power-voltage control. The second voltage reference value is obtained from reactive power-voltage control. This is the first output command value of the outer voltage loop. This is the second output command value of the outer voltage loop. This refers to the proportional gain coefficient of the voltage inner loop controller. This represents the integral gain coefficient of the voltage inner loop controller. This is the first output voltage reference value generated by the current inner loop control. This is the second output voltage reference value generated by the voltage inner loop control. For converter to control grid voltage Axial components, For converter to control grid voltage Axial components, Injecting grid current into the converter Axial components, Injecting grid current into the converter Axial components.

6. The control method for a grid-type high-voltage direct-connected energy storage system as described in claim 5, characterized in that, The harmonic components of the modular multilevel converter are adjusted by the circulating harmonic control module to reduce the losses caused by circulating current in the grid-connected direct-connected energy storage system. The specific expression is as follows: ； ； in, for Internal circulating current of modular multilevel converter For modular multilevel converters Phase upper arm current, For modular multilevel converters Lower bridge arm current, PR controls the proportional gain coefficient. The integral gain coefficient for PC control. This is the transfer function of a bandpass filter, used to obtain the harmonics in the circulating current.

7. The control method for a grid-type high-voltage direct-connected energy storage system as described in claim 6, characterized in that, The specific expression for adjusting the battery balance of the modular multilevel converter through the battery SOC balancing control module is as follows: ； ； ； ； ； ； ； in, for The total SOC of the battery phases, for The sum of the SOC of the upper bridge arm. for The sum of the SOC of the lower bridge arm, for Real-time average SOC of the upper and lower bridge arms for Mutually Real-time average SOC of the bridge arm This represents the real-time average SOC of each phase of the modular multilevel converter. For modular multilevel converters Real-time average value of phase SOC For modular multilevel converters Real-time average value of phase SOC For modular multilevel converters Real-time average value of phase SOC For the revised version Phase SOC power, The SOC equalization factor for each phase of the modular multilevel converter. The bridge arm SOC balance coefficient, for Mutually Corrected power of bridge arm battery energy storage for Mutually The rated output current of the bridge arm battery energy storage. for Mutually Real-time output power of the bridge arm battery energy storage, for Mutually Duty cycle of the DC / DC link for battery energy storage in the bridge arm. for Mutually Real-time output current of the bridge arm battery energy storage, The proportional gain of the outer loop PI element in the power circuit. The integral coefficient of the PI element in the power outer loop is denoted as . This is the proportional coefficient of the PI element in the inner current loop. is the integral coefficient of the PI element in the inner current loop.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the steps of the control method for the grid-type high-voltage direct-connected energy storage system according to any one of claims 4-7.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes the computer program, it executes the control method of the grid-type high-voltage direct-connected energy storage system according to any one of claims 4-7.

Images