Distributed energy storage type MMC structure and method based on uniform interval embedding

Abstract

The invention relates to the field of MMC converters, and discloses a distributed energy storage type MMC structure and method based on uniform interval embedding, and an upper bridge arm and a lower bridge arm are each composed of K sub-module groups; in each sub-module group of an upper bridge arm, a first sub-module close to a direct-current anode bus is set as an energy storage sub-module, and G SM sub-modules are sequentially cascaded at the rear stage of the energy storage sub-module; in each sub-module group of the lower bridge arm, a first sub-module close to a direct current cathode bus is set as an energy storage sub-module, and G SM sub-modules are sequentially cascaded at the preceding stage of the energy storage sub-module. According to the invention, the energy storage units are uniformly and dispersedly embedded into the specific sub-modules at intervals of a fixed number of sub-modules, so that the number, the embedding layout mode and the control strategy of the energy storage units are further optimized, the comprehensive performance of the energy storage type MMC can be brought into full play, the structural layout and the control difficulty can be simplified, the cost investment is reduced, and the energy storage type MMC is suitable for large-scale popularization and application. And the technical rationality and economical efficiency of the energy storage type MMC are synchronously optimized.

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 converter (MMC) has many advantages such as high modularity, easy expansion of voltage levels, and low harmonic content. It has gradually become an advantageous technical solution for long-distance, cross-regional high voltage direct current (HVDC) transmission and deep-sea offshore wind power transmission. However, MMC also faces many risks in engineering operation, such as frequent converter lockout due to grid-side faults, overvoltage of the DC system caused by power surplus on the DC side, and wind turbine disconnection caused by fault ride-through failure, which seriously affect the safety and reliability of the power system. Based on the advantages and characteristics of energy storage systems such as peak and frequency regulation, power fluctuation smoothing, power balance promotion, and inertia and frequency support, some scholars and experts have proposed integrating energy storage submodules (ESU) into the MMC structure in a centralized or decentralized manner to form an energy storage MMC (ES-MMC), so as to integrate the comprehensive characteristics of the energy storage system into the MMC. However, the energy storage submodules of centralized energy storage MMC need to withstand higher DC bus voltages, which makes it difficult to optimize design and operation and maintenance. When faced with a large number of submodules, the cost and investment of decentralized energy storage MMCs increase significantly, and the difficulty of controlling the charge state balance 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 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 comprising 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 being connected to a DC positive bus, the other end of the upper bridge arm being connected to one end of the lower bridge arm to form a common connection point, the common connection point being connected to an AC power supply, the other end of the lower bridge arm being connected to a DC negative bus, the upper bridge arm and the lower bridge arm being 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; K and G are both positive integers.

[0005] The present invention embeds energy storage units into specific submodules in a uniform and dispersed 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, which can not only give full play to the comprehensive performance of the energy storage type MMC, but also simplify its structural layout and control difficulty, reduce cost investment, and simultaneously optimize the technical rationality and economy of the energy storage type 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 embedded at uniform intervals, based on the distributed energy storage MMC structure embedded at uniform intervals of the optional implementation mode of the first aspect, the method comprising: performing charging and discharging 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 equivalent duty cycle; performing three-level capacitor voltage stratified balance control on the MMC structure based on system global voltage balance control, phase-to-phase voltage complementary balance control, and average voltage balance control of sub-modules within the phase based on energy storage sub-modules and SM sub-modules.

[0008] The present invention is designed through power flow and charge-discharge strategy design, voltage and current balance equation modeling, EUIDES-MMC active balance control design based on equivalent duty cycle, and three-level capacitor voltage hierarchical balance control strategy design based on system global voltage balance control, phase-to-phase voltage complementary balance control, and sub-module average voltage balance control based on ES-SM and SM. The EUIDES-MMC structure realizes that a certain number of energy storage cascade sub-modules can be included in the N upper and lower bridge arm sub-module strings put into operation in each time period of the same phase of the MMC, so that the energy storage cascade sub-modules are evenly distributed in the serial sequential input and removal timing process of all sub-modules of the single-phase bridge arm. It further ensures that the performance of the energy storage cascade sub-module is fully utilized in the entire working period, effectively realizes the power balance and capacitor voltage balance of EUIDES-MMC, and at the same time, the configuration number of the energy storage unit ES is reduced to the maximum, the structure of the energy storage MMC is simplified, the engineering cost is greatly saved, and it is conducive to improving the utilization rate of the energy storage capacity and the charge and discharge life, and has high engineering practicality and economy.

[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 of 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 DC side capacitor current cumulative value using the DC side capacitor voltage cumulative value of each sub-module; 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 sub-module current cumulative value; 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 implementation, for each phase bridge arm, active balance control is performed on the MMC structure, including: calculating the equivalent duty cycle of the DC-DC circuit of the energy storage submodule in a charging state 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; calculating the equivalent duty cycle of the DC-DC circuit of the energy storage submodule in a discharging state 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.

[0011] In an optional embodiment, the system global voltage balancing control includes: 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; 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; 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 each phase submodule.

[0012] In an optional embodiment, for each phase bridge arm, the inter-phase voltage complementary and balanced control includes: using the voltage negative sequence commutation components of the upper bridge arm and the lower bridge arm to calculate the DC current of the bridge arm loop; calculating 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 loop; performing PI control on the current correction values ​​of the upper bridge arm and the lower bridge arm to calculate the reference values ​​of the voltage negative sequence commutation components 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 submodule.

[0013] In an optional embodiment, the average voltage balancing control of the submodules within the phase of the energy storage submodule and the SM submodule includes: 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; 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.

[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 charging and discharging 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 equivalent duty cycle; a second control module, which is used to perform three-level capacitor voltage stratified balance control on the MMC structure based on system global voltage balance control, phase-to-phase voltage complementary balance control, and average voltage balance 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 execute the control method based on the uniformly spaced embedded distributed energy storage MMC 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 based on a uniformly spaced embedded distributed energy storage MMC structure of the above-mentioned 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 based on a uniformly spaced embedded distributed energy storage MMC structure of the second aspect or any corresponding embodiment thereof. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

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

[0020] Figure 2 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 based on a distributed energy storage MMC structure embedded at uniform intervals according to an embodiment of the present invention;

[0023] Figure 5 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 system global voltage balancing control block diagram according to an embodiment of the present invention;

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

[0027] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the 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 creative work are 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 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. The common connection point 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.

[0029] In each submodule group of the upper bridge arm, the first submodule close to the DC positive busbar is set as an energy storage submodule, and the rear stage of the energy storage submodule is cascaded with G SM submodules in sequence. In each submodule group of the lower bridge arm, the first submodule close to the DC negative busbar is set as an energy storage submodule, and the front stage of the energy storage submodule is cascaded with G SM submodules in sequence. K and G are both positive integers.

[0030] Specifically, refer to Figure 1 , since the bridge arm circuit of MMC is three-phase symmetrical, the A-phase bridge arm is taken as an example. The upper and lower bridge arms of the A-phase are symmetrical and consistent. The upper bridge arm and the lower bridge arm contain N submodules respectively. First, the first submodule close to the DC positive bus is set as an energy storage submodule (i.e., ES-SM). Then, the second ES-SM is set after every G SM submodules. All submodules of the upper bridge arm are set in the same way. That is, a submodule group consisting of 1 ES-SM and G SMs of 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 submodule settings are completed 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 setting of interval G needs to ensure that N is divisible by (G+1). The number of ES-SMs contained 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) put into operation, so the total number of ES-SMs contained 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 required energy consumption capacity or surplus capacity of the system, as shown in formula (2).

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

[0035] Among them, P res It represents the surplus capacity that EUIDES-MMC should have, which is used to absorb the transient redundant energy on the DC side; P stor It represents the energy storage capacity that EUIDES-MMC should have, which is used to configure the energy storage capacity that the system should have for smoothing output power, absorbing new energy or peak and frequency regulation. The larger capacity of the two is selected as the battery energy storage capacity for configuring ES-SM. Then the number ratio λ of ES-SM and its energy storage capacity ratio η are shown in 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 an 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 distributed energy storage MMC structure based on uniformly spaced embedding according to an optional implementation of the above embodiment is shown in FIG. 4( a ) and FIG. 4( b ). The method 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 charged and discharged and the power flow balance control, voltage and current balance control, and active balance control are performed.

[0043] Specifically, according to the topological structure 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 contains 6 ES charging states, 6 ES discharging states, and 2 ES balancing states. Each ES state corresponds to a power direction and flow balance. Among them, charging 1, charging 5, balancing 1, balancing 2, discharging 1, and discharging 5 correspond to the 6 most typical working modes of EUIDES-MMC. Among them, the charging 1 and charging 5 working modes can ensure that when EUIDES-MMC accumulates redundant power or energy on the DC side and AC side of the system, ES-SM can fully absorb and store excess surplus power or energy to ensure system balance and suppress system overvoltage; the discharging 1 and discharging 5 working modes can ensure that EUIDES-MMC actively releases energy when a fault occurs on the AC side and DC side of the system or a power shortage occurs, so as to supplement the required power shortage on the AC side and DC side of the system, and assist in supporting the system frequency, voltage, and suppressing power fluctuations. In the balancing 1 and balancing 5 working modes, the ES part stops charging and discharging, realizing 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 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 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, since the three-phase bridge arm circuit of the MMC is symmetrically balanced, the A-phase bridge arm is selected as an example for mathematical modeling. In the voltage balance in the abc stationary coordinate system, the voltage balance and current balance of a single bridge arm (upper bridge arm or lower bridge arm) can be expressed as shown in formula (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, respectively. my represents 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), 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 function of the i-th ES-SM submodule of the upper and lower bridge arms and the switching function of the j-th SM submodule, 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 of the energy storage submodule in a charging state 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; and (2) calculating the equivalent duty cycle of the DC-DC circuit of the energy storage submodule in a discharging state 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.

[0056] Specifically, according to Figure 1 The energy storage structure of ES-SM is cascaded with the basic SM submodule through the DC-DC circuit, which is conducive to the independent decoupling of charging and discharging, SOC balance and voltage regulation of the energy storage structure. The key to controlling the energy storage structure is to control the equivalent duty cycle of the switch in the DC-DC link, so as to determine the appropriate on and off time of 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 as 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 as 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 stratified balancing control.

[0066] The basic working mode of EUIDES-MMC is the rotation of successive input and removal of adjacent submodules of the upper and lower bridge arms. However, EUIDES-MMC contains a three-phase bridge arm circuit, each phase bridge arm circuit contains two upper and lower bridge arms, and the number of submodules is huge, including ES-SM and SM submodules of different structural types, resulting in the system AC and DC side voltages, the bridge arm circuit voltages of each phase, and the bridge arm submodule capacitor voltages all having different levels of differentiated voltage fluctuation characteristics. At the same time, each MMC submodule operates independently and the charging and discharging are not completely consistent, especially the ES-SM and SM submodules have obvious differences in structure and operation mode, resulting in a certain degree of imbalance in the capacitor voltages of the bridge arm submodules, especially the ES-SM and SM submodules.

[0067] To this end, a hierarchical balancing control strategy is adopted to gradually transition from the global system to the local system in view of the difference in capacitor voltage between the sub-modules of each phase and each bridge arm. 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) 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 values ​​of the bridge arm voltages of each phase, using PI control to obtain the d-axis reference value and q-axis reference value of the bridge arm current 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) based on the voltage balance equation of the single-phase equivalent loop and 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, 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 submodule.

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

[0072] After the above control steps, the obtained reference value of each phase bridge arm current i myref Substituting into formula (7), the reference values ​​u of the upper bridge arm and the 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 operation state of the submodule.

[0074] Specifically, since EUIDES-MMC is similar to MMC and also has interphase commutation, resulting in uneven voltage 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 influence of interphase negative sequence circulating current components on the interphase voltage balance of EUIDES-MMC.

[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-phase circuit respectively, I brmy It represents the effective value of the negative-sequence circulating current component of the y-arm current of the m-phase loop.

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

[0078]

[0079] Among them, umy2,ref represents the reference value of the voltage circulating current component of the y-bridge arm of the m-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 and SM submodules 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 consisting of one ES-SM and G SMs in a single-phase bridge arm 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 as 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 changes 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 uniformly spaced embedding. Through the design of power flow and charge-discharge strategy, voltage and current balance equation modeling, EUIDES-MMC active balance control design based on equivalent duty cycle, and capacitor voltage hierarchical balance control design, this structural design realizes that a certain number of energy storage cascade submodules can be included in the N upper and lower bridge arm submodule strings put into operation in each time period of the same phase of the MMC, so that the energy storage cascade submodules are evenly distributed in the serial sequential input and removal timing process of all submodules of the single-phase bridge arm. It further ensures that the performance of the energy storage cascade submodule is fully utilized in the entire working period, effectively realizes the power balance and capacitor voltage balance of EUIDES-MMC, that is, effectively realizes the relevant performance of the energy storage MMC, and at the same time, the configuration number of the energy storage submodule ES is reduced to the maximum, the structure of the energy storage MMC is simplified, and the engineering cost is greatly saved, and it is conducive to improving the utilization rate of the energy storage capacity and the charge and discharge life, and has high engineering practicality and economy.

[0091] In the present embodiment, a control device based on a distributed energy storage type MMC structure embedded at uniform intervals is also provided, and the device is used to implement the above-mentioned embodiments and preferred embodiments, and the descriptions that have been made will not be repeated. As used below, the term "module" can implement a combination of software and / or hardware of a predetermined function. Although the device described in the following embodiments is preferably implemented in software, the implementation of hardware, or a combination of software and hardware is also possible and conceived.

[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 perform charge and discharge control, power flow balance control, voltage and current balance control, and active balance control on the MMC structure through power flow and storage charge and discharge strategy design, voltage and current balance equation modeling, and active balance control of the energy storage type MMC structure based on 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, phase-to-phase voltage complementary balancing control, and phase-to-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 type MMC structure.

[0098] See also Figure 8 , Figure 8 is a schematic diagram of the structure 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, a memory 20, and interfaces for connecting various components, including high-speed interfaces and low-speed interfaces. Various components are connected to each other using different buses for communication, 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 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. Similarly, multiple computer devices can be connected, and each device provides some 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 a dedicated 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 executable 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, an application required for at least one function; the data storage area may store data created according to 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 arranged 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 comprises 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 method according to the embodiment of the present invention can be implemented in hardware, firmware, or can be implemented as a computer code that can be recorded in a storage medium, or can be implemented as a computer code that is originally stored in a remote storage medium or a non-temporary machine-readable storage medium and will be stored in a local storage medium through a network download, 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 hard disk, etc.; further, the storage medium can also include a combination of the above types of memories. 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 part 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 existence of the computer program instruction in a computer-readable medium includes, but is not limited to, a source file, an executable file, an installation package file, etc., and 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 accessible to the computer.

[0106] Although the embodiments of the present invention have been described in conjunction with 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, and such modifications and variations are all within the scope defined by the appended claims.

Claims

1. A distributed energy storage MMC structure based on uniformly spaced embedding, characterized in that: 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 a 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 an AC power supply, the other end of the lower bridge arm is connected to a DC negative bus, and the upper bridge arm and the lower bridge arm are both composed of K sub-module groups cascaded; In each submodule group of the upper bridge arm, the first submodule close to the DC positive busbar is set as an energy storage submodule, and the subsequent stage of the energy storage submodule is cascaded with G SM submodules in sequence; In each submodule group of the lower bridge arm, the first submodule close to the DC negative busbar is set as an energy storage submodule, and the front stage of the energy storage submodule is cascaded with G SM submodules in sequence; K and G are both positive integers.

2. The structure according to claim 1, characterized in that: 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.

3. A control method based on a distributed energy storage MMC structure embedded at uniform intervals, characterized in that: Based on the distributed energy storage MMC structure based on uniformly spaced embedding according to claim 2, 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 subjected to charge and discharge control, power flow balance control, voltage and current balance control, and active balance control; Based on system global voltage balancing control, inter-phase voltage complementary balancing control, and intra-phase sub-module average voltage balancing control based on energy storage sub-module and SM sub-module, the MMC structure is subjected to three-level capacitor voltage stratified balancing control.

4. The method according to claim 3, characterized in that: For each phase bridge arm, the MMC structure is subjected to voltage and current balance control, including: Based on the switching function and the DC side capacitor voltage of each submodule, the voltage equations of the upper bridge arm and the lower bridge arm are constructed; The accumulated value of the DC-side capacitor current is obtained by using the accumulated value of the DC-side capacitor voltage of each submodule; 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 energy storage submodule current, the bridge arm current equation is constructed; Based on the voltage equation of the upper bridge arm, the voltage equation of the lower bridge arm, and the bridge arm current equation, an equivalent circuit of a single-phase energy storage MMC structure is constructed; Based on the equivalent circuit of the single-phase energy storage MMC structure, a voltage balance equation of the single-phase equivalent circuit is obtained; The voltage balance equation of the single-phase equivalent circuit is used to perform voltage and current balance control on the MMC structure.

5. The method according to claim 3, characterized in that: For each phase bridge arm, the MMC structure is subjected to active power balance control, including: Calculate the equivalent duty cycle of the DC-DC circuit when the energy storage submodule is in a charging state 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; 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 a discharge state is calculated.

6. The method according to claim 4, characterized in that The system global voltage balancing control includes: The system global average bridge arm voltage is calculated based on the accumulated 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 voltages 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 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 the 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.

7. The method according to claim 3, characterized in that For each phase bridge arm, the inter-phase voltage complementary balancing control includes: The DC current of the bridge arm loop is calculated by using the negative sequence commutation components of the voltage of the upper bridge arm and the lower bridge arm; 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; Taking the difference between the 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 values ​​of the upper bridge arm and the lower bridge arm without negative sequence commutation components are used to control the operating state of the submodule.

8. The method according to claim 3, characterized in that 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 group 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.

9. A control device based on a distributed energy storage MMC structure embedded at uniform intervals, characterized in that: include: The first control module is used to perform charge and discharge control, power flow balance control, voltage and current balance control, and active balance control on the MMC structure through power flow and storage charge and discharge strategy design, voltage and current balance equation modeling, and active balance control of the energy storage type MMC structure based on 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, phase-to-phase voltage complementary balancing control, and phase-to-phase sub-module average voltage balancing control based on the energy storage sub-module and the SM sub-module.

10. 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 based on the uniformly spaced embedded distributed energy storage MMC structure according to any one of claims 3 to 8 by executing the computer instructions.

11. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores computer instructions, and the computer instructions 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 3 to 8.

12. A computer program product, characterized in that The method comprises computer instructions for causing a computer to execute the control method based on a uniformly spaced embedded distributed energy storage MMC structure according to any one of claims 3 to 8.

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