Distributed energy storage MMC structure and method based on uniformly spaced embedding

Abstract

The present invention relates to the field of MMC converters and discloses a distributed energy storage MMC structure and method based on uniformly spaced embedding. The upper and lower arms are each composed of K submodule clusters. In each submodule cluster of the upper arm, the first submodule closest to the DC positive busbar is set as an energy storage submodule, and the subsequent stage of the energy storage submodule is sequentially cascaded with G SM submodules. In each submodule cluster of the lower arm, the first submodule closest to the DC negative busbar is set as an energy storage submodule, and the preceding stage of the energy storage submodule is sequentially cascaded with G SM submodules. The present invention evenly and disperses energy storage units into specific submodules in the form of a fixed number of submodules per interval, thereby further optimizing the number of energy storage units, the embedding layout method, and the control strategy. This can fully utilize the comprehensive performance of the energy storage MMC, simplify its structural layout and control difficulty, reduce cost investment, and simultaneously optimize the technical rationality and economic efficiency of the energy storage MMC.

Description

Technical Field

[0001] The present invention relates to the field of MMC converters, and in particular to a distributed energy storage MMC structure and method based on uniformly spaced embedding. Background Art

[0002] Modular multilevel converters (MMCs) offer numerous advantages, including high modularity, easily scalable voltage levels, and low harmonic content. They have become a leading technical solution for long-distance, cross-regional high-voltage direct current (HVDC) transmission and deep-sea offshore wind power generation. However, MMCs also face numerous operational risks, including frequent converter lockouts during grid-side faults, DC system overvoltages caused by excess DC power, and wind turbine disconnection due to fault ride-through failures, all of which seriously impact the safety and reliability of power systems. Based on the advantages and characteristics of energy storage systems, such as peak and frequency regulation, power fluctuation mitigation, power balancing, and inertia and frequency support, some scholars and experts have proposed integrating energy storage units (ESUs) into MMC structures, either in a centralized or decentralized manner. This approach, known as ES-MMCs, integrates the comprehensive characteristics of energy storage systems into the MMC. However, the energy storage submodules of centralized energy storage MMCs must withstand higher DC bus voltages, making design and operation and maintenance optimization more challenging. Decentralized energy storage MMCs, when faced with a larger number of submodules, significantly increase costs and investment, and the difficulty of controlling the balanced state of charge of each energy storage submodule also increases significantly. Summary of the Invention

[0003] In view of this, the present invention provides a distributed energy storage MMC structure and method based on uniformly spaced embedding to solve the problem of difficulty in controlling the charge state balance of the energy storage submodules of the distributed energy storage MMC.

[0004] In a first aspect, the present invention provides a distributed energy storage MMC structure based on uniformly spaced embedding. The MMC structure includes three-phase bridge arms, each bridge arm is composed of an upper bridge arm and a lower bridge arm, one end of the upper bridge arm is connected to the DC positive bus, and the other end of the upper bridge arm is connected to one end of the lower bridge arm to form a common connection point, which is connected to an AC power supply, and the other end of the lower bridge arm is connected to the DC negative bus. The upper bridge arm and the lower bridge arm are both composed of K sub-module groups cascaded; in each sub-module group of the upper bridge arm, the first sub-module close to the DC positive bus is set as an energy storage sub-module, and the rear stage of the energy storage sub-module is cascaded with G SM sub-modules in sequence; in each sub-module group of the lower bridge arm, the first sub-module close to the DC negative bus is set as an energy storage sub-module, and the front stage of the energy storage sub-module is cascaded with G SM sub-modules in sequence; K and G are both positive integers.

[0005] The present invention embeds energy storage units into specific submodules in a uniformly distributed manner in the form of a fixed number of submodules per interval, thereby further optimizing the number of energy storage units, the embedding layout method, and the control strategy. This can not only fully utilize the comprehensive performance of the energy storage MMC, but also simplify its structural layout and control difficulty, reduce cost investment, and simultaneously optimize the technical rationality and economic efficiency of the energy storage MMC.

[0006] In an optional embodiment, the energy storage submodule includes: a DC-DC circuit, an energy storage power supply and a first converter, wherein one end of the DC-DC circuit is connected to the energy storage power supply, and the other end of the DC-DC circuit is connected to the DC side of the first converter; the AC side of the first converter is cascade-connected to the AC side of an adjacent SM submodule.

[0007] In the second aspect, the present invention provides a control method for a distributed energy storage MMC structure based on uniformly spaced embedding. Based on the distributed energy storage MMC structure based on uniformly spaced embedding of an optional implementation method of the first aspect, the method includes: through power flow and storage charge and discharge strategy design, voltage and current balance equation modeling, and active balance control of the energy storage MMC structure based on equivalent duty cycle, charging and discharging control, power flow balance control, voltage and current balance control, and active balance control are performed on the MMC structure; based on system global voltage balance control, phase-to-phase voltage complementary balance control, and average voltage balance control of the sub-module within the phase based on the energy storage sub-module and the SM sub-module, three-level capacitor voltage layered balance control is performed on the MMC structure.

[0008] The present invention utilizes power flow and charge-discharge strategy design, voltage and current balance equation modeling, EUIDES-MMC active power balance control based on equivalent duty cycle, and a three-level capacitor voltage tiered balance control strategy based on system-wide voltage balance control, interphase voltage complementary balance control, and intra-phase submodule average voltage balance control based on ES-SM and SM. The EUIDES-MMC structure ensures that each of the N upper and lower bridge arm submodule strings operating in each time period of the same MMC phase contains a certain number of energy storage cascade submodules, ensuring that the energy storage cascade submodules are evenly distributed throughout the serial switching on and off sequence of all submodules in the single-phase bridge arm. This further ensures that the performance of the energy storage cascade submodules is fully utilized throughout the entire operating period, effectively achieving EUIDES-MMC power balance and capacitor voltage balance. It also minimizes the number of energy storage units (ES) configured, simplifies the structure of the energy storage MMC, significantly saves engineering costs, and helps improve the utilization rate of energy storage capacity and charge-discharge life, resulting in high engineering practicality and economic efficiency.

[0009] In an optional embodiment, for each phase bridge arm, the MMC structure is subjected to voltage and current balance control, including: constructing voltage equations for the upper bridge arm and the lower bridge arm based on the switching function and the DC side capacitor voltage of each sub-module; obtaining the cumulative value of the DC side capacitor current using the cumulative value of the DC side capacitor voltage of each sub-module; constructing the bridge arm current equation based on the principle that the cumulative value of the DC side capacitor current is the sum of the single-phase bridge arm current and the cumulative value of the energy storage sub-module current; constructing the equivalent circuit of the single-phase energy storage MMC structure based on the voltage equation of the upper bridge arm, the voltage equation of the lower bridge arm, and the bridge arm current equation; obtaining the voltage balance equation of the single-phase equivalent loop based on the equivalent circuit of the single-phase energy storage MMC structure; and performing voltage and current balance control on the MMC structure using the voltage balance equation of the single-phase equivalent loop.

[0010] In an optional embodiment, for each phase bridge arm, active power balance control is performed on the MMC structure, including: calculating the equivalent duty cycle of the DC-DC circuit when the energy storage submodule is in a charging state based on the volt-second balance of the outlet voltage of the energy storage power supply and the ampere-second balance of the outlet current of the energy storage power supply; calculating the equivalent duty cycle of the DC-DC circuit when the energy storage submodule is in a discharging state based on the volt-second balance of the outlet voltage of the energy storage power supply and the ampere-second balance of the outlet current of the energy storage power supply.

[0011] In an optional embodiment, the global voltage balancing control of the system includes: calculating the global average bridge arm voltage of the system based on the cumulative values of the bridge arm sub-modules of all phase loops of the system; obtaining the d-axis reference value and q-axis reference value of the bridge arm current of each phase by using PI control based on the cumulative voltage reference values of the energy storage sub-modules and SM sub-modules of each phase of the system and the real-time value of the bridge arm voltage of each phase; performing Parker inverse transformation on the d-axis reference value and q-axis reference value of the bridge arm current of each phase to obtain the bridge arm current reference value of each phase; calculating the voltage reference value of the upper bridge arm and the lower bridge arm of each phase based on the voltage balance equation of the single-phase equivalent loop and the bridge arm current reference value of each phase, and the voltage reference value of the upper bridge arm and the lower bridge arm of each phase is used to control the operating state of the sub-module of each phase.

[0012] In an optional embodiment, for each phase bridge arm, the inter-phase voltage complementary balancing control includes: using the voltage negative-sequence commutation component of the upper bridge arm and the lower bridge arm to calculate the DC current of the bridge arm loop; calculating the current correction value of the upper bridge arm and the lower bridge arm according to the current reference value of the upper bridge arm and the lower bridge arm and the DC current of the bridge arm loop; performing PI control on the current correction value of the upper bridge arm and the lower bridge arm to calculate the reference value of the voltage negative-sequence commutation component of the upper bridge arm and the lower bridge arm; using the difference between the bridge arm voltage reference value of the upper bridge arm and the lower bridge arm and the reference value of the voltage negative-sequence commutation component of the upper bridge arm and the lower bridge arm as the voltage reference value of the upper bridge arm and the lower bridge arm without the negative-sequence commutation component; the voltage reference value of the upper bridge arm and the lower bridge arm without the negative-sequence commutation component is used to control the operating state of the sub-module.

[0013] In an optional embodiment, the average voltage balancing control of the sub-modules within the phase of the energy storage sub-module and the SM sub-module includes: calculating the total energy of each sub-module group in the upper bridge arm and the lower bridge arm; calculating the average energy of each sub-module in each sub-module group based on the total energy of each sub-module group in the upper bridge arm and the lower bridge arm; calculating the coordinated balancing capacitor voltage of each sub-module in each sub-module group using the average energy of each sub-module in each sub-module group; and controlling the output voltage of the energy storage sub-module to be the coordinated balancing capacitor voltage.

[0014] In the third aspect, the present invention provides a control device based on a distributed energy storage MMC structure embedded at uniform intervals, including: a first control module, which is used to perform charge and discharge control, power flow balance control, voltage and current balance control, and active power balance control on the MMC structure through power flow and storage charge and discharge strategy design, voltage and current balance equation modeling, and active power balance control of the energy storage MMC structure based on an equivalent duty cycle; a second control module, which is used to perform three-level capacitor voltage layered balancing control on the MMC structure based on system global voltage balancing control, phase-to-phase voltage complementary balancing control, and average voltage balancing control of sub-modules within the phase based on energy storage sub-modules and SM sub-modules.

[0015] In a fourth aspect, the present invention provides a computer device comprising: a memory and a processor, the memory and the processor being communicatively connected to each other, the memory storing computer instructions, and the processor executing the computer instructions to thereby execute the control method of the distributed energy storage MMC structure based on the uniformly spaced embedded structure of the above-mentioned second aspect or any corresponding embodiment thereof.

[0016] In a fifth aspect, the present invention provides a computer-readable storage medium having computer instructions stored thereon, the computer instructions being used to enable a computer to execute the control method of a distributed energy storage MMC structure based on uniformly spaced embedding according to the second aspect or any corresponding embodiment thereof.

[0017] In a sixth aspect, the present invention provides a computer program product comprising computer instructions for causing a computer to execute the control method of the distributed energy storage MMC structure based on uniformly spaced embedding according to the second aspect or any corresponding embodiment thereof. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are 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.

[0019] Figure 1 2 is a schematic diagram of the topological structure of EUIDES-MMC according to an embodiment of the present invention;

[0020] Figure 2 1 is a schematic diagram of the topological structure of the ES-SM submodule according to an embodiment of the present invention;

[0021] Figure 3 is a schematic diagram of the topological structure of the SM submodule according to an embodiment of the present invention;

[0022] 4( a ) and 4 ( b ) are flow charts of a control method for a distributed energy storage MMC structure based on uniformly spaced embedding according to an embodiment of the present invention;

[0023] Figure 5 1. It is a schematic diagram of the power flow balance of each side port of EUIDES-MMC according to an embodiment of the present invention;

[0024] Figure 6 is a single-phase equivalent circuit of EUIDES-MMC according to an embodiment of the present invention;

[0025] Figure 7is a block diagram of system global voltage balancing control according to an embodiment of the present invention;

[0026] Figure 8 Schematic diagram of the hardware structure of a computer device according to an embodiment of the present invention. DETAILED DESCRIPTION

[0027] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are 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 those skilled in the art without making creative efforts shall fall within the scope of protection of the present invention.

[0028] This embodiment provides a distributed energy storage MMC structure based on uniformly spaced embedding. The MMC structure includes three-phase bridge arms, each bridge arm consisting of an upper bridge arm and a lower bridge arm. One end of the upper bridge arm is connected to the DC positive bus, and the other end of the upper bridge arm is connected to one end of the lower bridge arm to form a common connection point. The common connection point is connected to the AC power supply, and the other end of the lower bridge arm is connected to the DC negative bus. The upper bridge arm and the lower bridge arm are both composed of K sub-module groups cascaded.

[0029] In each submodule cluster of the upper bridge arm, the first submodule closest to the DC positive busbar is configured as an energy storage submodule, and G SM submodules are sequentially connected in cascade to the subsequent stage of the energy storage submodule. In each submodule cluster of the lower bridge arm, the first submodule closest to the DC negative busbar is configured as an energy storage submodule, and G SM submodules are sequentially connected in cascade to the preceding stage of the energy storage submodule. K and G are both positive integers.

[0030] Specifically, refer to Figure 1 Since the bridge arm circuit of the MMC is three-phase symmetrical, we take the A-phase bridge arm as an example. The upper and lower bridge arms of phase A are symmetrical and consistent. The upper and lower bridge arms each contain N submodules. First, the first submodule close to the DC positive bus is set as an energy storage submodule (i.e., ES-SM). Then, a second ES-SM is set after every G SM submodules, and all submodules of the upper bridge arm are set in the same way. That is, a submodule group consisting of one ES-SM and G SMs in a single-phase bridge arm. Similarly, the first lower bridge arm submodule close to the DC negative bus is set as an ES-SM, and then all submodules are set based on the submodule setting method of the upper bridge arm. According to this setting method, the number K of ES-SMs contained in the upper bridge arm of phase A can be calculated by formula (1).

[0031]

[0032] The interval G must be set to ensure that N is divisible by (G + 1). The number of ES-SMs in the lower bridge arm of phase A is also K. That is, at each moment, phase A has N submodules (including K ES-SMs) in operation. Therefore, the total number of ES-SMs in the upper and lower bridge arms of phase A is 2K, containing a total of 2N submodules.

[0033] The battery energy storage capacity of each ES-SM can be set according to the energy consumption capacity or surplus capacity required by the system, as shown in formula (2).

[0034] S ES =max(P res , P stor ) / K (2)

[0035] Among them, P res P represents the surplus capacity that EUIDES-MMC should have, which is used to absorb the transient redundant energy on the DC side; stor The energy storage capacity of the EUIDES-MMC is used to configure the system for smoothing output power, absorbing new energy, or peak and frequency regulation. The larger of the two capacities is selected as the battery energy storage capacity for configuring the ES-SM. The proportion of the number of ES-SMs, λ, and their energy storage capacity, η, are then given by formula (3).

[0036]

[0037] Assume that the submodule packaging cost of a unit energy storage submodule is Cost sm , then compared with the traditional distributed energy storage MMC, EUIDES-MMC can save the submodule packaging cost:

[0038] ΔCost=2(NK)Cost sm (4)

[0039] Optionally, the energy storage submodule includes: a DC-DC circuit, an energy storage power supply and a first converter, wherein one end of the DC-DC circuit is connected to the energy storage power supply, and the other end of the DC-DC circuit is connected to the DC side of the first converter; the AC side of the first converter is cascade-connected to the AC side of the adjacent SM submodule.

[0040] Specifically, the specific topological structures of the energy storage submodule and the SM submodule are as follows: Figure 2 、 Figure 3 shown.

[0041] In this embodiment, a control method for a distributed energy storage MMC structure based on uniformly spaced embedding is provided. The control method for a distributed energy storage MMC structure based on uniformly spaced embedding according to an optional implementation of the above embodiment, as shown in FIG4( a ) and FIG4( b ), includes:

[0042] Step S1: Through the design of power flow and storage charge and discharge strategy, voltage and current balance equation modeling, and active balance control of energy storage MMC structure based on equivalent duty cycle, the MMC structure is subjected to charge and discharge control, power flow balance control, voltage and current balance control, and active balance control.

[0043] Specifically, according to the topology of the uniformly embedded distributed energy storage MMC (Embedded at Uniform Intervals of Distributed Energy Storage MMC, EUIDES-MMC) and the ES-SM structure, the power balancing port of EUIDES-MMC includes the DC side power P dc , energy storage side power P es , AC side power P ac The power of each side port can flow in both directions, such as Figure 5 shown.

[0044] While maintaining system power balance, ES can match the three basic states of charging, balancing, and discharging required for operating in different working conditions, as shown in Table 1.

[0045] Table 1

[0046]

[0047] According to Table 1, EUIDES-MMC includes six ES charging states, six ES discharging states, and two ES balancing states. Each ES state corresponds to a power direction and flow balance. Charge 1, Charge 5, Balance 1, Balance 2, Discharge 1, and Discharge 5 correspond to the six most typical EUIDES-MMC operating modes. Charge 1 and Charge 5 modes ensure that when EUIDES-MMC accumulates redundant power or energy on the DC and AC sides of the system, the ES-SM can fully absorb and store excess power or energy, maintaining system balance and mitigating overvoltage. Discharge 1 and Discharge 5 modes ensure that when faults or power shortages occur on the AC or DC sides of the system, the EUIDES-MMC proactively releases energy to supplement the required power on the AC and DC sides, assisting in maintaining system frequency and voltage, and mitigating power fluctuations. In Balance 1 and Balance 5 modes, ES partially ceases charging and discharging, enabling direct communication and mutual assistance between the AC and DC sides of the system.

[0048] Optionally, for each phase bridge arm, the MMC structure is subjected to voltage and current balance control, including: (1) constructing voltage equations of the upper bridge arm and the lower bridge arm based on the switching function and the DC side capacitor voltages of each submodule; (2) obtaining the DC side capacitor current cumulative value using the DC side capacitor voltage cumulative value of each submodule; (3) constructing the bridge arm current equation based on the principle that the DC side capacitor current cumulative value is the sum of the single-phase bridge arm current and the energy storage submodule current cumulative value; (4) constructing an equivalent circuit of the single-phase energy storage type MMC structure based on the voltage equation of the upper bridge arm, the voltage equation of the lower bridge arm, and the bridge arm current equation; (5) obtaining the voltage balance equation of the single-phase equivalent circuit based on the equivalent circuit of the single-phase energy storage type MMC structure; (6) using the voltage balance equation of the single-phase equivalent circuit to perform voltage and current balance control on the MMC structure.

[0049] Specifically, because the three-phase bridge arm circuit of the MMC is symmetrically balanced, phase A is selected as an example for mathematical modeling. The voltage balance in the abc stationary coordinate system, and the voltage and current balance of a single bridge arm (upper or lower arm) can be expressed as shown in Equation (5).

[0050]

[0051] Among them, U esi with U smj They represent the DC link capacitor voltage of the i-th ES-SM submodule and the DC link capacitor voltage of the j-th SM submodule, u my The accumulated submodule AC side voltage of the upper and lower bridge arms of the mth phase (y=p represents the upper bridge arm, y=n represents the lower bridge arm) is represented by i br represents the current of a single bridge arm, i esi Represents the energy storage output current of the i-th ES-SM submodule. S y Represents the switching function of the upper and lower bridge arms, and S esi With S smj They represent the switching functions of the i-th ES-SM submodule and the j-th SM submodule of the upper and lower bridge arms, respectively, as shown in formula (6).

[0052]

[0053] The equivalent circuit of single-phase EUIDES-MMC is as follows: Figure 6 As shown. Figure 6 , the voltage balance equation of the single-phase equivalent circuit is shown in formula (7).

[0054]

[0055] Optionally, for each phase bridge arm, the MMC structure is subjected to active power balance control, including: (1) calculating the equivalent duty cycle of the DC-DC circuit when the energy storage submodule is in a charging state based on the volt-second balance of the outlet voltage of the energy storage power supply and the ampere-second balance of the outlet current of the energy storage power supply; (2) calculating the equivalent duty cycle of the DC-DC circuit when the energy storage submodule is in a discharging state based on the volt-second balance of the outlet voltage of the energy storage power supply and the ampere-second balance of the outlet current of the energy storage power supply.

[0056] Specifically, according to Figure 1 The ES-SM's energy storage structure is cascaded with the basic SM submodule via a DC-DC circuit, enabling independent and decoupled charging and discharging, SOC balancing, and voltage regulation within the energy storage structure. The key to controlling the energy storage structure lies in controlling the equivalent duty cycle of the DC-DC link, thereby determining the appropriate on- and off-times for the DC-DC switch.

[0057] When ES is in charging state, the DC-DC circuit connected in series with ES is in Buck working mode. At this time, the output voltage U es The volt-second balance and the export current I for the energy storage power supply es The ampere-second balance can be expressed as shown in formula (8).

[0058]

[0059] It can be concluded that the equivalent duty ratio of the DC-DC circuit when ES is in the charging state is shown in formula (9).

[0060]

[0061] When ES is in the discharge state, the DC-DC circuit connected in series with ES is in the Boost working mode. At this time, the output voltage U es The volt-second balance and the export current I for the energy storage power supply es The ampere-second balance can be expressed as shown in formula (10).

[0062]

[0063] It can be concluded that the equivalent duty ratio of the DC-DC link when ES is in the discharge state is shown in formula (11).

[0064]

[0065] Step S2: Based on the system global voltage balancing control, inter-phase voltage complementary balancing control, and intra-phase sub-module average voltage balancing control based on the energy storage sub-module and the SM sub-module, the MMC structure is subjected to three-level capacitor voltage layered balancing control.

[0066] The basic operating mode of the EUIDES-MMC is the alternating switching between adjacent submodules in the upper and lower arms. However, the EUIDES-MMC comprises a three-phase arm circuit, each consisting of an upper and lower arm. The large number of submodules, including ES-SM and SM submodules of varying structural types, results in differential voltage fluctuations at varying levels in the system's AC and DC voltages, the voltages in each phase arm circuit, and the capacitor voltages of the arm submodules. Furthermore, each MMC submodule operates independently, and its charging and discharging are not completely consistent. In particular, the ES-SM and SM submodules exhibit significant structural and operational differences, leading to a degree of imbalance in the capacitor voltages between the arm submodules, particularly between the ES-SM and SM submodules.

[0067] To this end, in view of the differences in capacitor voltages between the sub-modules of each phase and each bridge arm, a hierarchical balancing control strategy is adopted that gradually transitions from the global system to the local system. At different control levels, three-level capacitor voltage hierarchical balancing control strategies are implemented, including the system global voltage balancing control of EUIDES-MMC, the phase-to-phase voltage complementary balancing control, and the average voltage balancing control of the sub-modules within the phase based on ES-SM and SM.

[0068] Optionally, the system global voltage balancing control includes: (1) calculating the system global average bridge arm voltage based on the cumulative values of the bridge arm submodules of all phase loops of the system; (2) obtaining the d-axis reference value and q-axis reference value of the bridge arm current of each phase by using PI control based on the cumulative voltage reference values of the energy storage submodules and SM submodules of each phase of the system and the real-time value of the bridge arm voltage of each phase; (3) performing Parker inverse transformation on the d-axis reference value and q-axis reference value of the bridge arm current of each phase to obtain the bridge arm current reference value of each phase; (4) calculating the voltage reference value of the upper bridge arm and the lower bridge arm of each phase based on the voltage balance equation of the single-phase equivalent loop and the bridge arm current reference value of each phase, and the voltage reference value of the upper bridge arm and the lower bridge arm of each phase is used to control the operating state of the submodule of each phase.

[0069] The system global average bridge arm voltage U is calculated based on the cumulative value of the bridge arm submodules of all phase loops of the system. gav , as shown in formula (12).

[0070]

[0071] refer to Figure 7 , the accumulated voltage reference value of the submodules of ES-SM and SM of each phase of the system is taken as U gav is the real-time value of each phase bridge arm voltage, which generates the d-axis reference value i of each phase bridge arm current after the PI control link. dyref With the q-axis reference value i qyref, and then after Parker inverse transformation, the reference value of each phase bridge arm current i is obtained myref (i ayref ,i byref ,i mcyref ).

[0072] After the above control steps, the reference value of each phase bridge arm current i myref When substituting into formula (7), the reference values u of the upper bridge arm and lower bridge arm of each phase can be calculated respectively: my,ref (y=p,n).

[0073] Optionally, for each phase bridge arm, the inter-phase voltage complementary balancing control includes: (1) using the voltage negative sequence commutation component of the upper bridge arm and the lower bridge arm to calculate the DC current of the bridge arm loop; (2) calculating the current correction value of the upper bridge arm and the lower bridge arm according to the current reference value of the upper bridge arm and the lower bridge arm and the DC current of the bridge arm loop; (3) performing PI control on the current correction value of the upper bridge arm and the lower bridge arm to calculate the reference value of the voltage negative sequence commutation component of the upper bridge arm and the lower bridge arm; (4) using the difference between the bridge arm voltage reference value of the upper bridge arm and the lower bridge arm and the reference value of the voltage negative sequence commutation component of the upper bridge arm and the lower bridge arm as the voltage reference value of the upper bridge arm and the lower bridge arm without the negative sequence commutation component; (5) the voltage reference value of the upper bridge arm and the lower bridge arm without the negative sequence commutation component is used to control the operating state of the submodule.

[0074] Specifically, since EUIDES-MMC is similar to MMC and also has interphase commutation, which causes voltage imbalance between phases, on the basis of the system global voltage balance control, interphase voltage complementary balance control is further implemented to weaken or eliminate the impact of the interphase negative sequence circulating current component on the EUIDES-MMC interphase voltage balance.

[0075]

[0076] Among them, Δi brmy ,i brmy,ref They represent the correction value and reference value of the Y bridge arm current of the m-phase loop, P dcm with U dcm They represent the DC active power and DC voltage of the m-th phase circuit, I brmy It represents the effective value of the negative-sequence circulating current component of the Y-arm current of the m-th phase loop.

[0077] PI control is performed on the y-arm current correction value of the m-phase loop to obtain the reference value of the negative-sequence circulating current component of the m-phase voltage, as shown in formula (14).

[0078]

[0079] Among them, umy2,ref The reference value of the voltage circulating current component of the Y bridge arm of the m-th phase loop, k bp With k bi They represent the proportional coefficient and integral coefficient of PI control respectively.

[0080] In this way, the reference value of the bridge arm voltage without the negative-sequence circulating current component can be obtained by subtracting the reference value of the negative-sequence circulating current component from the bridge arm voltage of the m-th phase voltage, as shown in formula (15).

[0081] u my1,ref =u my,ref -u my2,ref (15)

[0082] Optionally, for each phase bridge arm, the intra-phase submodule average voltage balancing control based on the energy storage submodule and the SM submodule includes: (1) calculating the total energy of each submodule group in the upper bridge arm and the lower bridge arm; calculating the average energy of each submodule in each submodule group based on the total energy of each submodule group in the upper bridge arm and the lower bridge arm; (2) calculating the coordinated balancing capacitor voltage of each submodule in each submodule group using the average energy of each submodule in each submodule group; and controlling the output voltage of the energy storage submodule to be the coordinated balancing capacitor voltage.

[0083] Due to the differences in the structure and operation mode of the ES-SM and SM submodules, in order to ensure energy sharing, coordinated operation and smooth transition between the ES-SM and SM submodules, the average voltage balancing control of the submodules within the phase of the ES-SM submodule and the SM submodule is adopted. As mentioned above, the DC-DC link of the ES-SM submodule realizes the decoupling control of the AC side and the DC side of the submodule, which can fully utilize the energy storage efficiency of the ES. Figure 1 The total energy S of a submodule group composed of 1 ES-SM and G SMs in a single-phase bridge arm is smg It can be expressed as shown in formula (16).

[0084] S smg =U es I es +(G+1)(KI es -I dc / 3)U sm (16)

[0085] Then the average energy of a single submodule within a submodule cluster is shown in formula (17).

[0086]

[0087] It can be obtained that the coordinated balancing capacitor voltage U of ES-SM and SM coeq Should be controlled as:

[0088]

[0089] That is, the ES-SM submodule should convert U es Control transfer to U coeq , thereby controlling and changing the bridge arm current of the phase, and then converting the SM submodule voltage into U coeq .

[0090] The present invention proposes a distributed energy storage MMC topology, EUIDES-MMC, based on evenly spaced embedding. Through power flow and charge-discharge strategy design, voltage and current balance equation modeling, EUIDES-MMC active power balance control based on equivalent duty cycle, and capacitor voltage layered balance control, this structural design ensures that each of the N upper and lower bridge arm submodule strings operating in each time period of the same MMC phase contains a certain number of energy storage cascade submodules, ensuring that the energy storage cascade submodules are evenly distributed throughout the serial switching on and off sequence of all submodules in the single-phase bridge arm. This further ensures the full performance of the energy storage cascade submodules throughout the entire operating period, effectively achieving power balance and capacitor voltage balance in the EUIDES-MMC, effectively achieving the relevant performance of the energy storage MMC. It also minimizes the number of energy storage submodules configured, simplifies the structure of the energy storage MMC, significantly saves engineering costs, and helps improve the utilization rate of energy storage capacity and charge-discharge life, resulting in high engineering practicality and economic efficiency.

[0091] In this embodiment, a control device based on a distributed energy storage MMC structure embedded at uniform intervals is also provided. The device is used to implement the above-mentioned embodiments and preferred embodiments, and the details already described will not be repeated. As used below, the term "module" can be a combination of software and / or hardware that implements a predetermined function. Although the devices described in the following embodiments are preferably implemented in software, implementation using hardware, or a combination of software and hardware, is also possible and contemplated.

[0092] This embodiment provides a control device based on a distributed energy storage MMC structure embedded at uniform intervals, including:

[0093] The first control module is used to control the charge and discharge, power flow, voltage and current balance, and active power balance of the MMC structure through power flow and storage charge and discharge strategy design, voltage and current balance equation modeling, and active power balance control of the energy storage MMC structure based on an equivalent duty cycle;

[0094] The second control module is used to perform three-level capacitor voltage stratification balancing control on the MMC structure based on system global voltage balancing control, inter-phase voltage complementary balancing control, and intra-phase sub-module average voltage balancing control based on the energy storage sub-module and the SM sub-module.

[0095] The further functional description of each of the above modules and units is the same as that of the above corresponding embodiments and will not be repeated here.

[0096] The control device based on the evenly spaced embedded distributed energy storage MMC structure in this embodiment is presented in the form of a functional unit, where the unit refers to an ASIC (Application Specific Integrated Circuit) circuit, a processor and memory that executes one or more software or fixed programs, and / or other devices that can provide the above functions.

[0097] An embodiment of the present invention further provides a computer device having the above-mentioned control device based on the evenly spaced embedded distributed energy storage MMC structure.

[0098] See also Figure 8 , Figure 8 is a structural diagram of a computer device provided by an optional embodiment of the present invention, such as Figure 8 As shown, the computer device includes: one or more processors 10, memory 20, and interfaces for connecting various components, including high-speed interfaces and low-speed interfaces. Various components utilize different buses to communicate with each other and can be installed on a common mainboard or installed in other ways as needed. The processor can process the instructions executed in the computer device, including instructions stored in the memory or on the memory to display the graphical information of the GUI on an external input / output device (such as, a display device coupled to the interface). In some optional embodiments, if necessary, multiple processors and / or multiple buses can be used together with multiple memories and multiple memories. Equally, multiple computer devices can be connected, and each device provides part of the necessary operations (for example, as a server array, a group of blade servers, or a multi-processor system). Figure 8 A processor 10 is taken as an example.

[0099] The processor 10 may be a central processing unit, a network processor, or a combination thereof. The processor 10 may further include a hardware chip. The hardware chip may be an application-specific integrated circuit, a programmable logic device, or a combination thereof. The programmable logic device may be a complex programmable logic device, a field programmable gate array, a general purpose array logic, or any combination thereof.

[0100] The memory 20 stores instructions that can be executed by at least one processor 10, so that the at least one processor 10 executes the method shown in the above embodiment.

[0101] The memory 20 may include a program storage area and a data storage area, wherein the program storage area may store an operating system and application programs required for at least one function; the data storage area may store data created based on the use of the computer device, etc. In addition, the memory 20 may include a high-speed random access memory, and may also include a non-transient memory, such as at least one disk storage device, a flash memory device, or other non-transient solid-state storage device. In some optional embodiments, the memory 20 may optionally include a memory remotely located relative to the processor 10, and these remote memories may be connected to the computer device via a network. Examples of the above-mentioned network include, but are not limited to, the Internet, an intranet, a local area network, a mobile communication network, and combinations thereof.

[0102] The memory 20 may include a volatile memory, such as a random access memory; the memory may also include a non-volatile memory, such as a flash memory, a hard disk or a solid-state drive; the memory 20 may also include a combination of the above types of memory.

[0103] The computer device further includes a communication interface 30 for the computer device to communicate with other devices or a communication network.

[0104] The embodiment of the present invention also provides a computer-readable storage medium. The above-mentioned method according to the embodiment of the present invention can be implemented in hardware, firmware, or implemented as a computer code that can be recorded in a storage medium, or implemented as a computer code that is originally stored in a remote storage medium or a non-temporary machine-readable storage medium and downloaded through a network and will be stored in a local storage medium, so that the method described herein can be stored in such software processing on a storage medium using a general-purpose computer, a dedicated processor, or programmable or dedicated hardware. Among them, the storage medium can be a magnetic disk, an optical disk, a read-only storage memory, a random access memory, a flash memory, a hard disk or a solid-state drive, etc.; further, the storage medium can also include a combination of the above-mentioned types of memory. It can be understood that a computer, a processor, a microprocessor controller or programmable hardware includes a storage component that can store or receive software or computer code. When the software or computer code is accessed and executed by a computer, a processor or hardware, the method shown in the above embodiment is implemented.

[0105] A portion of the present invention may be applied as a computer program product, such as a computer program instruction, which, when executed by a computer, can call or provide the method and / or technical solution according to the present invention through the operation of the computer. Those skilled in the art should understand that the form in which the computer program instruction exists in a computer-readable medium includes, but is not limited to, a source file, an executable file, an installation package file, etc. Accordingly, the way in which the computer program instruction is executed by the computer includes, but is not limited to: the computer directly executes the instruction, or the computer compiles the instruction and then executes the corresponding compiled program, or the computer reads and executes the instruction, or the computer reads and installs the instruction and then executes the corresponding installed program. Here, the computer-readable medium may be any available computer-readable storage medium or communication medium that can be accessed by the computer.

[0106] Although the embodiments of the present invention have been described with reference to the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention. Such modifications and variations are all within the scope defined by the appended claims.

Claims

1. A control method based on a distributed energy storage MMC structure embedded in uniform intervals, characterized in that: The MMC structure includes a three-phase bridge arm, each bridge arm is composed of an upper bridge arm and a lower bridge arm, one end of the upper bridge arm is connected to the DC positive bus, the other end of the upper bridge arm is connected to one end of the lower bridge arm to form a common connection point, the common connection point is connected to the AC power supply, and the other end of the lower bridge arm is connected to the DC negative bus, and the upper bridge arm and the lower bridge arm are both composed of K sub-module groups cascaded; in each sub-module group of the upper bridge arm, the first sub-module close to the DC positive bus is set as an energy storage sub-module, and the rear stage of the energy storage sub-module is sequentially cascaded with G SM sub-modules; in each sub-module group of the lower bridge arm, the first sub-module close to the DC negative bus is set as an energy storage sub-module, and the front stage of the energy storage sub-module is sequentially cascaded with G SM sub-modules; The energy storage submodule includes: a DC-DC circuit, an energy storage power supply, and a first converter, wherein one end of the DC-DC circuit is connected to the energy storage power supply, and the other end of the DC-DC circuit is connected to the DC side of the first converter; the AC side of the first converter is cascade-connected to the AC side of the adjacent SM submodule; K and G are both positive integers; The method comprises: Through the design of power flow and storage charge and discharge strategy, voltage and current balance equation modeling, and active balance control of energy storage MMC structure based on equivalent duty cycle, the MMC structure is controlled for charge and discharge, power flow balance control, voltage and current balance control, and active balance control; Based on the system global voltage balancing control, inter-phase voltage complementary balancing control, and intra-phase sub-module average voltage balancing control based on the energy storage sub-module and the SM sub-module, the MMC structure is subjected to three-level capacitor voltage layered balancing control; For each phase bridge arm, the MMC structure is subjected to voltage and current balance control, including: constructing voltage equations for the upper bridge arm and the lower bridge arm based on the switching function and the DC side capacitor voltages of each submodule; obtaining the cumulative value of the DC side capacitor current using the accumulated value of the DC side capacitor voltage of each submodule; constructing the bridge arm current equation based on the principle that the accumulated value of the DC side capacitor current is the sum of the accumulated value of the single-phase bridge arm current and the accumulated value of the energy storage submodule current; constructing an equivalent circuit of the single-phase energy storage MMC structure based on the voltage equation of the upper bridge arm, the voltage equation of the lower bridge arm, and the bridge arm current equation; obtaining the voltage balance equation of the single-phase equivalent loop based on the equivalent circuit of the single-phase energy storage MMC structure; and performing voltage and current balance control on the MMC structure using the voltage balance equation of the single-phase equivalent loop.

2. The method according to claim 1, characterized in that For each phase bridge arm, active power balance control is performed on the MMC structure, including: Calculate the equivalent duty cycle of the DC-DC circuit when the energy storage submodule is in a charging state based on the volt-second balance of the output voltage of the energy storage power supply and the ampere-second balance of the output current of the energy storage power supply; According to the volt-second balance of the outlet voltage of the energy storage power supply and the ampere-second balance of the outlet current of the energy storage power supply, the equivalent duty cycle of the DC-DC circuit when the energy storage submodule is in the discharge state is calculated.

3. The method according to claim 1, characterized in that The system global voltage balancing control includes: The system global average bridge arm voltage is calculated based on the cumulative values of the bridge arm submodules of all phase loops of the system; Based on the accumulated voltage reference values of the energy storage submodules and SM submodules of each phase of the system and the real-time values of the bridge arm voltage of each phase, the d-axis reference value and q-axis reference value of the bridge arm current of each phase are obtained by using PI control; Performing a Parker inverse transformation on the d-axis reference value and the q-axis reference value of the bridge arm current of each phase to obtain a bridge arm current reference value of each phase; Based on the voltage balance equation of the single-phase equivalent circuit and the current reference value of each phase bridge arm, the voltage reference value of the upper bridge arm and the lower bridge arm of each phase is calculated, and the voltage reference value of the upper bridge arm and the lower bridge arm of each phase is used to control the operating state of each phase sub-module.

4. The method according to claim 1, wherein For each phase bridge arm, the inter-phase voltage complementary balancing control includes: The DC current of the bridge arm circuit is calculated using the negative sequence commutation components of the voltages of the upper and lower bridge arms; Calculate the current correction values of the upper bridge arm and the lower bridge arm according to the current reference values of the upper bridge arm and the lower bridge arm and the DC current of the bridge arm circuit; Performing PI control on the current correction values of the upper bridge arm and the lower bridge arm to calculate reference values of the voltage negative sequence commutation components of the upper bridge arm and the lower bridge arm; The difference between the upper bridge arm and the lower bridge arm voltage reference value and the reference value of the voltage negative sequence commutation component of the upper bridge arm and the lower bridge arm is used as the voltage reference value of the upper bridge arm and the lower bridge arm without the negative sequence commutation component; The voltage reference values of the upper bridge arm and the lower bridge arm that do not contain negative sequence commutation components are used to control the operating state of the submodule.

5. The method according to claim 1, wherein For each phase bridge arm, the intra-phase sub-module average voltage balancing control based on the energy storage sub-module and the SM sub-module includes: Calculate the total energy of each submodule cluster in the upper bridge arm and the lower bridge arm; Based on the total energy of each submodule cluster in the upper bridge arm and the lower bridge arm, the average energy of each submodule in each submodule cluster is calculated; Calculate the coordinated balancing capacitor voltage of each submodule in each submodule cluster using the average energy of each submodule in each submodule cluster; The output voltage of the energy storage submodule is controlled to be the coordinated balancing capacitor voltage.

6. A control device based on a distributed energy storage MMC structure embedded at uniform intervals, characterized in that: The control method of the distributed energy storage MMC structure based on uniformly spaced embedding according to any one of claims 1 to 5 comprises: The first control module is used to control the charge and discharge, power flow, voltage and current balance, and active power balance of the MMC structure through power flow and storage charge and discharge strategy design, voltage and current balance equation modeling, and active power balance control of the energy storage MMC structure based on an equivalent duty cycle; The second control module is used to perform three-level capacitor voltage stratification balancing control on the MMC structure based on system global voltage balancing control, inter-phase voltage complementary balancing control, and intra-phase sub-module average voltage balancing control based on the energy storage sub-module and the SM sub-module.

7. A computer device, characterized in that: include: A memory and a processor, wherein the memory and the processor are communicatively connected to each other, the memory stores computer instructions, and the processor executes the control method of the distributed energy storage MMC structure based on uniformly spaced embedding according to any one of claims 1 to 5 by executing the computer instructions.

8. A computer-readable storage medium, characterized in that The computer-readable storage medium stores computer instructions, which are used to enable a computer to execute the control method based on a uniformly spaced embedded distributed energy storage MMC structure according to any one of claims 1 to 5.

9. A computer program product, characterized in that The method comprises computer instructions for causing a computer to execute the control method of the distributed energy storage MMC structure based on uniformly spaced embedding according to any one of claims 1 to 5.

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