A network-constructing HC-EVSC device and a super-energy capacity dispersion equalization configuration method thereof

Abstract

A network construction HC-EVSC device and a super-capacity energy dispersion equalization configuration method, n parallel super-capacity energy storage branches are configured on the inverter side; according to the active power variation and power recovery time of the MMC adopting the network construction control strategy under the grid frequency step, the number of super-capacity energy storage branches put into operation is determined; according to the active power shortage of the MMC adopting the network construction control strategy, the total transmission power of all super-capacity energy storage branches and the energy coefficient of each super-capacity energy storage branch are determined, and the output power instruction of the super-capacity energy storage branch is determined according to the total transmission power and the energy coefficient; when the output power instruction of the super-capacity energy storage branch meets the maximum power support level constraint, the active power output by each super-capacity energy storage branch is dynamically adjusted according to the output power instruction, the super-capacity energy dispersion equalization configuration is realized, the problem of insufficient rotational inertia and reactive power support capacity of the hybrid cascaded power transmission system is effectively solved, and the operation reliability and stability of the hybrid cascaded power transmission system are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of ultra-high voltage direct current (UHVDC) transmission, and specifically relates to a network-building hybrid cascade-energy storage voltage source converter (HC-EVSC) topology with inertia support performance and a method for distributing and balancing super-capacitor energy. Background Art

[0002] LCC (Low-Channel Conversion) DC transmission technology, with its numerous advantages, including high transmission capacity, strong economical efficiency, and mature technology, has been widely used in large-capacity, long-distance transmission scenarios. However, commutation failure in inverter-side LCCs has limited its application. Compared to LCC technology, flexible DC transmission technology based on modular multilevel converters (MMCs) offers advantages such as no commutation failure and flexible control methods. However, this technology requires a higher investment compared to LCC technology. Combining the technical advantages of both LCCs and MMCs, the Baihetan-Jiangsu UHV project utilizes a sending-end LCC and a receiving-end LCC connected in series with three parallel MMCs to achieve 800kV / 8000MW power transmission. This hybrid cascaded DC transmission system provides reactive power support for the LCCs at the inverter station, reducing the risk of LCC commutation failure. Furthermore, the LCC converters can block the fault current in the MMCs during DC faults, making it a promising technology for future application.

[0003] In the existing technology, the traditional MMC converter adopts a grid-following control strategy, which exhibits current source characteristics. It cannot track load power fluctuations and needs to rely on a strong grid for operation. It is suitable for a grid environment dominated by synchronous generators. The grid-forming control shows a voltage source external characteristic similar to that of a synchronous generator. It can operate in an autonomous network and actively support the grid frequency / voltage. It is suitable for new power systems with high power electronics. The MMC part adopts grid-forming control to maintain the stability of the DC bus voltage, which is conducive to the stable and reliable operation of the LCC. However, in order to provide sufficient inertia and reactive power support, the converter power changes significantly during the transient period. The required transient power will cause a sudden change in the power of the station, and the station will present a high overload state, which seriously threatens the safe and stable operation of the flexible DC equipment. Therefore, it is necessary to propose a hybrid cascade topology and its control method suitable for new power systems. Summary of the Invention

[0004] To address the deficiencies in the prior art, the present invention provides a networked HC-EVSC device with inertia support performance and a method for distributing and balancing excess capacity energy. Based on a hybrid cascaded DC transmission topology, the networked HC-EVSC device installs excess capacity branches on the MMC DC side and implements distributed and balanced energy configuration of the excess capacity branches under decentralized coordination. This effectively addresses the issues of insufficient rotational inertia and reactive power support capabilities of the hybrid cascaded transmission system, thereby improving the operational reliability and stability of the hybrid cascaded transmission system.

[0005] The present invention adopts the following technical solutions.

[0006] The present invention proposes a networked HC-EVSC device, which uses a structure in which multiple parallel modular multilevel converters are cascaded with a phase-commutation converter on the inverter side. The device includes: n parallel super-capacity energy storage branches configured on the inverter side, where n is a positive integer; one end of each super-capacity energy storage branch is connected to the positive electrode of the DC line, and the other end is connected to the ground electrode of the DC line;

[0007] The device also includes: an excess energy balancing controller and n excess energy storage branch controllers; the excess energy balancing controller is configured to determine the number of excess energy storage branches to be put into operation based on the active power change and power recovery time of the modular multilevel converter adopting the network control strategy under the grid frequency step; determine the total transmission power of all excess energy storage branches and the energy coefficient of each excess energy storage branch based on the active power shortage of the modular multilevel converter adopting the network control strategy, and send the total transmission power and the energy coefficient of each excess energy storage branch to the corresponding excess energy storage branch controller respectively;

[0008] The excess energy storage branch controller is used to determine the output power instruction of the excess energy storage branch based on the received total transmission power and energy coefficient; when the output power instruction of the excess energy storage branch meets the maximum power support level constraint, the excess energy storage branch controller adjusts the active power output of each excess energy storage branch according to the output power instruction.

[0009] Each supercapacitor energy storage branch includes multiple supercapacitor submodules connected in series; each supercapacitor submodule includes a power device and a supercapacitor cluster.

[0010] The super-capacity energy balancing controller includes: a super-capacity energy storage branch parameter configuration module;

[0011] The excess energy storage branch parameter configuration module is used to determine the maximum current of all excess energy storage branches based on the active power change and power recovery time of the modular multilevel converter adopting the grid control strategy under the grid frequency step; and use the maximum current and the rated current of each excess energy storage branch to determine the number of excess energy storage branches connected in parallel.

[0012] The super-capacity energy storage branch parameter configuration module includes: frequency step acquisition unit, simulation unit, branch current calculation unit, and branch quantity calculation unit;

[0013] A frequency step acquisition unit, used to obtain a maximum frequency step value of an AC system connected to a modular multilevel converter adopting a network control strategy;

[0014] a simulation unit for determining, by a simulation method, a maximum active power variation of the modular multilevel converters adopting a network control strategy at a maximum frequency step value and a power recovery time required for the active power to recover to the rated active power in a scenario where all modular multilevel converters output rated active power and are not connected to an overcapacity energy storage branch;

[0015] A branch current calculation unit is configured to use the maximum active power variation output by the simulation unit as the maximum active power supported by all the over-capacity energy storage branches, and the power recovery time output by the simulation unit as the support time of all the over-capacity energy storage branches; and to calculate the maximum current of all the over-capacity energy storage branches using the maximum active power supported by all the over-capacity energy storage branches, the support time, and the rated voltage of each over-capacity energy storage branch; wherein the DC bus voltage is the rated voltage of each over-capacity energy storage branch;

[0016] a branch quantity calculation unit, configured to: if the maximum current of all the excess energy storage branches is not greater than the maximum current carrying capacity of the power device, then the number of the excess energy storage branches is 1; if the maximum current of all the excess energy storage branches is greater than the maximum current carrying capacity of the power device, then determine the number of the excess energy storage branches connected in parallel based on the maximum current of all the excess energy storage branches and the rated current of each excess energy storage branch; wherein the rated current of each excess energy storage branch is determined based on the current carrying capacity and overload capacity of the power device in each excess energy storage branch.

[0017] The maximum current of all overcapacity energy storage branches satisfies the following relationship:

[0018]

[0019] Where, I SCmax is the maximum current of all overcapacity energy storage branches, ΔP max is the maximum active power supported by all overcapacity energy storage branches, ΔT max is the support time of all overcapacity energy storage branches, V SCN is the rated voltage of each super-capacity energy storage branch.

[0020] The super-capacity energy balancing controller further includes: an energy balancing control module;

[0021] An energy balance control module is configured to determine total transmission power of all over-capacity energy storage branches and energy coefficients of the over-capacity energy storage branches according to an active power shortage of the modular multilevel converter adopting the network construction control strategy, and send the total transmission power and the energy coefficients of the over-capacity energy storage branches to corresponding over-capacity energy storage branch controllers respectively.

[0022] The energy balance control module comprises a total transmission power calculation unit.

[0023] The total transmission power calculation unit is configured to take a difference between an active power output by the modular multilevel converter adopting the network construction control strategy and an active power reference value as the active power shortage, and take the active power shortage as the total transmission power of all the over-capacity energy storage branches.

[0024] The total transmission power of all the over-capacity energy storage branches satisfies the following relationship:

[0025] ΔP SC =P mmc -P mmc_ref

[0026] In the formula, ΔP SC is the total transmission power of all the over-capacity energy storage branches, P mmc is the active power output by the modular multilevel converter adopting the network construction control strategy, and P mmc_ref is the active power reference value of the modular multilevel converter adopting the network construction control strategy.

[0027] The energy balance control module further comprises an energy coefficient balance configuration unit.

[0028] The energy coefficient balance configuration unit is configured to assign the maximum value α′ to an energy coefficient of an over-capacity energy storage branch having the shortest electrical distance from the receiving end converter station among all the over-capacity energy storage branches, and assign equal values α″ to energy coefficients of the remaining over-capacity energy storage branches, and satisfy α′+(n-1)α″=1.

[0029] The energy coefficients of the over-capacity energy storage branches are used to calculate output power instructions of the over-capacity energy storage branches, and the adjustment cost and the adjustment duration of each over-capacity energy storage branch are determined based on the output power instructions of the over-capacity energy storage branches.

[0030] The adjustment cost and the adjustment duration of each over-capacity energy storage branch are optimized through multiple iterations, and the energy coefficients of the over-capacity energy storage branches are optimized, so that the adjustment cost and the adjustment duration of each over-capacity energy storage branch are optimal, and the adjustment cost and the adjustment duration of all the over-capacity energy storage branches are optimal, and the sum of the output power instructions of all the over-capacity energy storage branches satisfies the total transmission power of all the over-capacity energy storage branches. i , i=1, 2, …, n, and satisfy

[0031] The objective function satisfies the following relationship:

[0032]

[0033] In the formula, F is the objective function, λ is the weight, C i , τ i are the adjustment cost and adjustment time of the i-th overcapacity energy storage branch in response to the output power instruction, and C i =f(ΔP i ), τ i =f(ΔP i ), ΔP i is the difference between the actual output power value of the i-th over-capacity energy storage branch and the output power command, and f() represents the functional relationship;

[0034] The sum of the output power instructions of all excess energy storage branches satisfies the total transmission power of all excess energy storage branches as a constraint condition, and satisfies the following relationship:

[0035]

[0036] Where, is the output power instruction of the i-th overcapacity energy storage branch, ΔP SC is the total transmission power of all super-capacity energy storage branches.

[0037] The super-capacity energy storage branch controller includes: an output power instruction generation module;

[0038] An output power instruction generation module is used to determine the output power instruction of the excess energy storage branch based on the received total transmission power and energy coefficient; when the output power instruction of the excess energy storage branch meets the maximum power support level constraint, the excess energy storage branch controller adjusts the active power output of each excess energy storage branch according to the output power instruction;

[0039] When the output power instruction of the excess energy storage branch does not meet the maximum power support level constraint, the active power output by the excess energy storage branch is maintained at the maximum power support level, and a signal is sent to the excess energy balancing controller to re-optimize the energy coefficient of each excess energy storage branch.

[0040] The output power instruction of the overcapacity energy storage branch determined by the output power instruction generation module should meet the maximum power support level constraint shown in the following relationship:

[0041]

[0042] Where, is the output power instruction of the i-th super-capacity energy storage branch, PSC_imax is the maximum power support level of the i-th over-capacity energy storage branch under the rated DC voltage of the receiving-end converter station. The maximum power support level of each over-capacity energy storage branch is determined according to the current-carrying capacity and overload capacity of the power devices in each over-capacity energy storage branch under the rated voltage.

[0043] The super-capacity energy storage branch controller further includes: a super-capacity sub-module parameter configuration module;

[0044] The super-capacitor module parameter configuration module is used to establish an equivalent circuit of the super-capacitor energy storage branch before adjusting the active power output of each super-capacitor energy storage branch according to the output power instruction. The equivalent circuit includes an equivalent capacitor and an equivalent internal resistance. Based on the equivalent circuit, when the power released by the equivalent capacitor is not less than the sum of the power consumed by the equivalent internal resistance and the active power demand of the super-capacitor energy storage branch, the number of super-capacitor sub-modules connected in series in the super-capacitor energy storage branch is determined according to the output power instruction, the open-circuit voltage and the equivalent capacitance value.

[0045] The supercapacitor module parameter configuration module includes: an equivalent circuit establishment unit;

[0046] The equivalent circuit establishment unit is used to establish the equivalent circuit of each super-capacitor energy storage branch. The equivalent circuit is an ideal capacitor and an ideal resistor in series. The ideal capacitor value is the equivalent capacitance value C when all super-capacitor sub-modules in all super-capacitor energy storage branches are put into operation. SC_i The ideal resistance is the equivalent internal resistance R when all supercapacitor modules in all supercapacitor energy storage branches are put into operation. SC_i ;

[0047] The power consumed by the equivalent internal resistance of the i-th supercapacitor energy storage branch satisfies the following relationship:

[0048]

[0049] Where, P SCR_i is the power consumed by the equivalent internal resistance of the i-th supercapacitor energy storage branch, I SCN_i is the rated current of the i-th supercapacity energy storage branch, R SC_i is the equivalent internal resistance of the i-th supercapacity energy storage branch, ΔT max The support time of all overcapacity energy storage branches;

[0050] The power released by the equivalent capacitance of the i-th supercapacitor energy storage branch satisfies the following relationship:

[0051] P SCC_i ≥P SCN_i +P SCR_i

[0052] Where, P SCC_iP SCN_i is the active power demand of the i-th over-capacity energy storage branch based on the equivalent circuit, satisfying ΔP max is the maximum active power supported by all over-capacity energy storage branches.

[0053] The over-capacity sub-module parameter configuration module further comprises an over-capacity sub-module quantity calculation unit.

[0054] In the over-capacity sub-module quantity calculation unit, the equivalent capacitance value in the over-capacity energy storage branch satisfies the following relationship:

[0055]

[0056] In the formula, V SC_i is the open circuit voltage of the i-th over-capacity energy storage branch, V SCN is the rated voltage of each over-capacity energy storage branch, is the output power instruction of the i-th over-capacity energy storage branch.

[0057] In combination with the voltage withstand capability of the over-capacity cluster in the over-capacity sub-module and the equipment insulation level, the open circuit voltage V SC_i of the i-th over-capacity energy storage branch is selected. SC_i The equivalent capacitance value C SC_i is reserved for the redundant over-capacity cluster, and the number of over-capacity sub-modules in series in each over-capacity energy storage branch is determined.

[0058] The over-capacity energy storage branch controller further comprises an active power balancing control module.

[0059] In the active power balancing control module, the active power P SC_i output by the i-th over-capacity energy storage branch is compared with the ratio of the DC bus voltage V dc at the receiving end converter station to obtain the DC current reference value I dc_refi of the i-th over-capacity energy storage branch; the difference between the current I SC_i of the i-th over-capacity energy storage branch and the DC current reference value I dc_refi is subjected to PI control to obtain a value, which is summed with the DC bus voltage V dc at the receiving end converter station to obtain the voltage reference value of the i-th over-capacity energy storage branch; the ratio of the voltage reference value of the i-th over-capacity energy storage branch to the average voltage V SC_sm of each over-capacity sub-module in the i-th over-capacity energy storage branch is used to determine the number of over-capacity sub-modules to be put into the i-th over-capacity energy storage branch, and according to the number of over-capacity sub-modules to be put in, a switching pulse is generated by a modulation link to trigger the corresponding over-capacity sub-module in the i-th over-capacity energy storage branch.

[0060] The present invention also proposes a method for distributing and balancing super-capacity energy of a networked HC-EVSC device, comprising:

[0061] Collect the DC bus voltage as the rated voltage of each over-capacity energy storage branch;

[0062] The excess energy balancing controller determines the maximum current of all excess energy storage branches based on the active power change and power recovery time of the modular multilevel converters using the grid control strategy under grid frequency steps. It also determines the number of excess energy storage branches to be put into operation using the maximum current and the rated current of each excess energy storage branch.

[0063] The excess energy balancing controller determines the total transmission power of all excess energy storage branches and the energy coefficient of each excess energy storage branch according to the active power shortage of the modular multi-level converter adopting the network control strategy; and sends the total transmission power and the energy coefficient of each excess energy storage branch to the corresponding excess energy storage branch controller.

[0064] The excess energy storage branch controller determines the output power instruction of the excess energy storage branch based on the received total transmission power and energy coefficient. When the output power instruction of the excess energy storage branch meets the maximum power support level constraint, the excess energy storage branch controller dynamically adjusts the active power output of each excess energy storage branch according to the output power instruction.

[0065] An equivalent circuit is established for each super-capacitive energy storage branch, which includes an equivalent capacitor and an equivalent internal resistance. Based on the equivalent circuit, when the power released by the equivalent capacitor is not less than the sum of the power consumed by the equivalent internal resistance and the active power demand of the super-capacitive energy storage branch, the number of super-capacitive sub-modules connected in series in the super-capacitive energy storage branch is determined according to the output power command, open-circuit voltage, and equivalent capacitance value.

[0066] The present invention also provides a terminal, comprising a processor and a storage medium; the storage medium is used to store instructions; and the processor is used to operate according to the instructions to execute steps of the method.

[0067] The present invention also relates to a computer-readable storage medium having a computer program stored thereon, which implements the steps of the method when the program is executed by a processor.

[0068] The beneficial effects of the present invention are as follows: compared with the prior art, the grid-forming HC-EVSC device proposed in the present invention improves the inertia support and reactive power compensation capabilities of the converter for the system under fault conditions of the inverter-side AC system by configuring an overcapacity energy storage branch on the inverter side and performing distributed and balanced control of the overcapacity energy. At least one MMC converter on the inverter side adopts a grid-forming control strategy to adjust the converter transmission power according to changes in system frequency and voltage, thereby achieving active and reactive power support for the AC power grid.

[0069] By optimizing the balanced configuration of the energy coefficients of the branches, the maximum energy coefficient of the supercapacitor branch with the shortest electrical distance to the receiving converter station is achieved, which is the basis for improving the dynamic response speed, while the balance of the remaining energy coefficients is the basis for achieving stable active power support. Through the feedback optimization of the energy coefficient, the problem of insufficient active power support caused by the active power shortage caused by the failure of a supercapacitor branch that continuously outputs at the maximum power support level is avoided. Moreover, through the feedback optimization of the energy coefficient, the goal of balanced energy configuration of each supercapacitor branch is ultimately achieved, the service life of each supercapacitor branch is improved, and it is conducive to the standardized construction and operation and maintenance of each supercapacitor branch. On the basis of achieving the dispersed and balanced configuration of supercapacitor energy, the number of supercapacitor submodules connected in series in each supercapacitor branch is further determined, the utilization rate of supercapacitor submodules in each supercapacitor branch is increased, the redundant number of supercapacitor submodules is reduced, and the construction cost is effectively controlled. BRIEF DESCRIPTION OF THE DRAWINGS

[0070] Figure 1 This is a topological diagram of a networked HC-EVSC device with inertial support performance proposed in an embodiment of the present invention;

[0071] Figure 2 A topological diagram of the MMC in an embodiment of the present invention;

[0072] Figure 3 Schematic block diagram of a converter grid-type control strategy based on a virtual synchronous machine in an embodiment of the present invention;

[0073] Figure 4 This is a block diagram of the balanced control of the active power output by each over-capacity energy storage branch proposed in an embodiment of the present invention;

[0074] Figure 5 This is a waveform diagram of the active power simulation of the MMC converter under frequency step in an embodiment of the present invention. DETAILED DESCRIPTION

[0075] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. The embodiments described in this application are only part of the embodiments of the present invention, not all of them. Based on the spirit of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0076] The present invention proposes a grid-connected HC-EVSC device with inertia support performance, which adopts a hybrid cascaded DC transmission topology. The rectifier side adopts a line-commuted converter (LCC), and the inverter side adopts a structure in which multiple parallel modular multilevel converters (MMCs) and one line-commutated converter are cascaded. N parallel super-capacity energy storage branches are configured on the inverter side, where n is a positive integer. One end of each super-capacity energy storage branch is connected to the positive electrode of the DC line, and the other end is connected to the ground electrode of the DC line.

[0077] Taking into account the overload capacity of the rectifier-side equipment and the DC bus voltage fluctuations during transient faults, at least one overcapacity energy storage branch is directly connected to the MMC side. The overcapacity branch parameter configuration is determined by calculating the transient active power / energy constraint equation of the flexible DC converter station and combining it with the device overload level. The overcapacity energy storage branch equipment tracks the changes in active power on the inverter side in real time and adjusts the power compensation amount in real time according to the changes in transmission power to support the MMC DC side voltage, reduce the risk of LCC commutation failure, effectively improve the system's fault recovery characteristics, and ensure the safe and reliable operation of the system.

[0078] In the embodiment, Figure 1 As shown in the figure, the rectifier side adopts dual 12-pulse LCCs, and the inverter side adopts a structure of three parallel MMCs and one LCC cascaded. The rectifier side is connected to the receiving converter station through a DC bus, and the LCC and MMC are connected to the AC grid through corresponding transformers.

[0079] The three parallel MMCs have the same structure. Each phase bridge arm includes a bridge arm inductor, a bridge arm resistor and the same number of sub-modules in series. The sub-modules are composed of multiple full-bridge and half-bridge sub-modules. In the embodiment, the topology of each MMC is as follows: Figure 2 As shown in the figure, the MMC is connected to the common connection point PCC (Point of Common Coupling) of the AC power grid through a transformer. The MMC adopts a three-phase six-bridge structure, and the number of sub-modules SM connected in series in each bridge arm is N, L arm With R arm are the bridge arm inductance and bridge arm resistance respectively, u va 、u vb 、u vc is the three-phase voltage on the AC side, i sa 、i sb 、i sc is the three-phase current on the AC side, i pa 、i pb 、i pc is the three-phase current of the upper bridge arm, i na 、i nb 、i ncFor the lower bridge arm three-phase current, P and N are positive and negative.

[0080] The inverter side configured with the MMC is configured with n super-capacity energy storage branches, and n is a positive integer. Figure 1 As shown in the figure, each super-capacity energy storage branch includes a plurality of super-capacity sub-modules in series; each super-capacity sub-module includes a power device and a super-capacity cluster; in the embodiment, the super-capacity energy storage branch includes m super-capacity sub-modules CM1, CM2, …, CMm, and m is a positive integer; one end of the super-capacity energy storage branch is connected with the positive pole of the DC line, and the other end of the super-capacity energy storage branch is connected with the grounding pole of the DC line.

[0081] At least one of the three MMCs adopts a network construction control strategy; in the embodiment, any one MMC adopts a constant voltage control strategy, and the other two MMCs adopt a constant power control strategy. In the device proposed in the application, at least one MMC adopts a network construction control strategy, the MMC adopting the network construction control strategy does not depend on the external AC system voltage to realize synchronization, and behaves as a synchronous machine, adjusts the converter transmission power value according to the frequency and voltage changes of the inverter side, and realizes active and reactive power characteristics of the AC power grid; moreover, the MMC adopting the network construction control strategy changes the real-time output power value during the transient state, the super-capacity energy storage branch receives the power change instruction from the MMC adopting the network construction control strategy, and real-time tracks the change of the converter transmission power.

[0082] Figure 3 A schematic block diagram of the network construction control strategy of the converter based on the virtual synchronous machine is shown in Figure 3 (a), P ref is a given active power reference value, P m is the actual measured MMC active power, ω g is the actual measured angular frequency, ω0 is the rated angular frequency of the system, D is the damping coefficient, H is the inertia time constant, and θ is the phase angle reference value. As shown in Figure 3 (b), Q ref is a given reactive power reference value, Q m is the actual measured MMC reactive power, Dq is the reactive droop coefficient, E0 is the internal potential amplitude, and E is the internal potential amplitude reference value; the three-phase modulation voltage of the MMC is determined according to the phase angle reference value and the internal potential amplitude reference value.

[0083] The network-constructing HC-EVSC device further comprises an over-capacity energy equalization controller and n over-capacity energy storage branch controllers; the over-capacity energy equalization controller is configured to determine the number of over-capacity energy storage branches to be put into according to the active power variation and power recovery time of the modular multilevel converter adopting the network-constructing control strategy under a grid frequency step; determine the total transmission power of all over-capacity energy storage branches and the energy coefficients of each over-capacity energy storage branch according to the active power shortage of the modular multilevel converter adopting the network-constructing control strategy, and send the total transmission power and the energy coefficients of each over-capacity energy storage branch to the corresponding over-capacity energy storage branch controller respectively;

[0084] Specifically, the over-capacity energy equalization controller comprises an over-capacity energy storage branch parameter configuration module and an energy equalization control module.

[0085] The over-capacity energy storage branch parameter configuration module is configured to determine the current maximum value of all over-capacity energy storage branches according to the active power variation and power recovery time of the modular multilevel converter adopting the network-constructing control strategy under a grid frequency step; and determine the number of over-capacity energy storage branches in parallel by using the current maximum value and the rated current of each over-capacity energy storage branch.

[0086] The over-capacity energy storage branch parameter configuration module comprises a frequency step acquisition unit, a simulation unit, a branch current calculation unit and a branch number calculation unit; wherein,

[0087] The frequency step acquisition unit is configured to obtain the maximum frequency step value of the AC system connected to the modular multilevel converter adopting the network-constructing control strategy.

[0088] The simulation unit is configured to determine the maximum value of the active power variation of the modular multilevel converter adopting the network-constructing control strategy under the maximum frequency step value and the power recovery time required for the active power to recover to the rated active power in a scenario where all modular multilevel converters output rated active power and are not connected to over-capacity energy storage branches by using a simulation method.

[0089] The branch current calculation unit is configured to take the maximum value of the active power variation output by the simulation unit as the maximum active power supported by all over-capacity energy storage branches, and take the power recovery time output by the simulation unit as the support time of all over-capacity energy storage branches; and calculate the current maximum value of all over-capacity energy storage branches by using the maximum active power supported by all over-capacity energy storage branches, the support time and the rated voltage of each over-capacity energy storage branch; wherein the DC bus voltage is the rated voltage of each over-capacity energy storage branch.

[0090] The current maximum value of all over-capacity energy storage branches satisfies the following relationship:

[0091]

[0092] Where, I SCmax is the maximum current of all overcapacity energy storage branches, ΔP max is the maximum active power supported by all overcapacity energy storage branches, ΔT max is the support time of all overcapacity energy storage branches, V SCN is the rated voltage of each overcapacity energy storage branch;

[0093] a branch quantity calculation unit, configured to: if the maximum current of all the excess energy storage branches is not greater than the maximum current carrying capacity of the power device, then the number of the excess energy storage branches is 1; if the maximum current of all the excess energy storage branches is greater than the maximum current carrying capacity of the power device, then determine the number of the excess energy storage branches connected in parallel based on the maximum current of all the excess energy storage branches and the rated current of each excess energy storage branch; wherein the rated current of each excess energy storage branch is determined based on the current carrying capacity and overload capacity of the power device in each excess energy storage branch.

[0094] In the networking HC-EVSC device proposed in this invention, an excess energy balancing controller is used to adjust the number of excess energy storage branches put into operation in real time according to the power changes of the modular multilevel converter adopting the networking control strategy. This achieves the decentralized configuration of excess energy in a flexible and changeable manner, provides active support to the receiving converter station, and ensures system stability.

[0095] A2) An energy balancing control module is configured to determine the total transmission power of all excess energy storage branches and the energy coefficient of each excess energy storage branch based on the active power shortage of the modular multilevel converter adopting the network control strategy; and to send the total transmission power and the energy coefficient of each excess energy storage branch to the corresponding excess energy storage branch controller.

[0096] Energy balancing control module, including: total transmission power calculation unit, energy coefficient balancing configuration unit;

[0097] a total transmission power calculation unit, configured to use the difference between the active power output by the modular multilevel converter adopting the network control strategy and the active power reference value as the active power deficit, and use the active power deficit as the total transmission power of all excess energy storage branches;

[0098] The total transmission power of all super-capacity energy storage branches satisfies the following relationship:

[0099] ΔP SC =P mmc -P mmc_ref

[0100] Where, ΔP SC is the total transmission power of all super-capacity energy storage branches, P mmc is the active power output by the MMC using the network control strategy, Pmmc_ref active power reference value output by the MMC adopting the network construction control strategy;

[0101] An energy coefficient equalization configuration unit is configured to assign the energy coefficient of the super-capacity energy storage branch with the shortest electrical distance from the receiving end converter station as the maximum value, i.e., a', and the value range of a' is [0.8, 1.0]; the energy coefficients of the remaining super-capacity energy storage branches are equal, i.e., a'', and a' + (n-1)a'' = 1 is satisfied.

[0102] The output power instruction of each super-capacity energy storage branch is calculated by using the assigned energy coefficient of each super-capacity energy storage branch; and the adjustment cost and adjustment time length of each super-capacity energy storage branch are determined based on the output power instruction of each super-capacity energy storage branch.

[0103] The energy coefficients of the super-capacity energy storage branches are optimized by multiple iterations, with the comprehensive optimization of the adjustment cost and adjustment time length of each super-capacity energy storage branch and the comprehensive optimization of the adjustment cost and adjustment time length of all super-capacity energy storage branches as the objective function, and the sum of the output power instructions of all super-capacity energy storage branches satisfying the total transmission power of all super-capacity energy storage branches as the constraint condition; and the optimized energy coefficients of the super-capacity energy storage branches are a i , i = 1, 2,..., n, and a

[0104] The objective function satisfies the following relationship:

[0105]

[0106] In the formula, F is the objective function, λ is the weight, C i , τ i are the adjustment cost and adjustment time length of the i-th super-capacity energy storage branch in response to the output power instruction, respectively, and C i = f(ΔP i ), τ i = f(ΔP i ), ΔP i is the difference between the current output power actual value and the output power instruction of the i-th super-capacity energy storage branch, and f() represents a function relationship.

[0107] The sum of the output power instructions of all super-capacity energy storage branches satisfies the total transmission power of all super-capacity energy storage branches as the constraint condition, and satisfies the following relationship:

[0108]

[0109] In the formula, is the output power instruction of the i-th super-capacity energy storage branch, and ΔP SC is the total transmission power of all super-capacity energy storage branches.

[0110] On the basis of realizing the decentralized configuration of supercapacity energy by utilizing the supercapacity energy storage branch parameter configuration module, the energy balance control module determines and optimizes the energy coefficient of each branch, and assigns the maximum value to the energy coefficient of the supercapacity energy storage branch with the shortest electrical distance to the receiving converter station, so as to improve the response speed of power support, and achieve the optimal comprehensive adjustment cost and adjustment time of each supercapacity energy storage branch, and the optimal comprehensive adjustment cost and adjustment time of all supercapacity energy storage branches, so as to realize the energy balanced configuration of each supercapacity energy storage branch under the optimal economic benefit. Moreover, the process of determining and optimizing the energy coefficient of each branch by the energy balance control module is carried out before sending a signal to the supercapacity energy storage branch controller, and the constraint condition is that the sum of the output power instructions of all supercapacity energy storage branches meets the total transmission power of all supercapacity energy storage branches, which becomes the prerequisite for avoiding output power oscillation of each supercapacity energy storage branch.

[0111] The excess energy storage branch controller is used to determine the output power instruction of the excess energy storage branch based on the received total transmission power and energy coefficient; when the output power instruction of the excess energy storage branch meets the maximum power support level constraint, the excess energy storage branch controller adjusts the active power output of each excess energy storage branch according to the output power instruction.

[0112] Specifically, the super-capacity energy storage branch controller includes: an output power instruction generation module, a super-capacity sub-module parameter configuration module, and an active power balancing control module;

[0113] B1) an output power instruction generation module, configured to determine an output power instruction for the excess energy storage branch based on the received total transmission power and energy coefficient; when the output power instruction of the excess energy storage branch meets the maximum power support level constraint, the excess energy storage branch controller adjusts the active power outputted by each excess energy storage branch according to the output power instruction;

[0114] When the output power command of the excess energy storage branch does not meet the maximum power support level constraint, the active power output by the excess energy storage branch is maintained at the maximum power support level, and a signal is sent to the excess energy balancing controller to re-optimize the energy coefficient of each excess energy storage branch;

[0115] The output power instruction of the overcapacity energy storage branch determined by the output power instruction generation module should meet the maximum power support level constraint shown in the following relationship:

[0116]

[0117] Where, is the output power instruction of the i-th super-capacity energy storage branch, P SC_imaxis the maximum power support level of the i-th over-capacity energy storage branch under the rated DC voltage of the receiving-end converter station. The maximum power support level of each over-capacity energy storage branch is determined according to the current-carrying capacity and overload capacity of the power devices in each over-capacity energy storage branch under the rated voltage.

[0118] B2) A super-capacitor module parameter configuration module is used to establish an equivalent circuit for the super-capacitor energy storage branch before adjusting the active power output of each super-capacitor energy storage branch according to the output power instruction. The equivalent circuit includes an equivalent capacitor and an equivalent internal resistance. Based on the equivalent circuit, when the power released by the equivalent capacitor is not less than the sum of the power consumed by the equivalent internal resistance and the active power demand of the super-capacitor energy storage branch, the number of super-capacitor modules connected in series in the super-capacitor energy storage branch is determined according to the output power instruction, the open-circuit voltage, and the equivalent capacitance value.

[0119] A supercapacitor module parameter configuration module includes: an equivalent circuit establishment unit and a supercapacitor module quantity calculation unit;

[0120] The equivalent circuit establishment unit is used to establish the equivalent circuit of each super-capacitor energy storage branch. The equivalent circuit is an ideal capacitor and an ideal resistor in series. The ideal capacitor value is the equivalent capacitance value C when all super-capacitor sub-modules in all super-capacitor energy storage branches are put into operation. SC_i The ideal resistance is the equivalent internal resistance R when all supercapacitor modules in all supercapacitor energy storage branches are put into operation. SC_i ;

[0121] The power consumed by the equivalent internal resistance of the i-th supercapacitor energy storage branch satisfies the following relationship:

[0122]

[0123] Where, P SCR_i is the power consumed by the equivalent internal resistance of the i-th supercapacitor energy storage branch, I SCN_i is the rated current of the i-th supercapacity energy storage branch, R SC_i is the equivalent internal resistance of the i-th supercapacity energy storage branch, ΔT max The support time of all overcapacity energy storage branches;

[0124] The power released by the equivalent capacitance of the i-th supercapacitor energy storage branch satisfies the following relationship:

[0125] P SCC_i ≥P SCN_i +P SCR_i

[0126] Where, P SCC_i is the power released by the equivalent capacitance of the i-th supercapacitor energy storage branch, P SCN_iis the active power demand of the i-th super-capacity energy storage branch based on the equivalent circuit, satisfying ΔP max It is the maximum active power supported by all overcapacity energy storage branches.

[0127] In the super-capacitor module quantity calculation unit, the equivalent capacitance value in the super-capacitor energy storage branch is determined to satisfy the following relationship:

[0128]

[0129] Where V SC_i is the open circuit voltage of the i-th supercapacitor energy storage branch, V SCN is the rated voltage of each super-capacity energy storage branch, is the output power instruction of the i-th overcapacity energy storage branch;

[0130] Combined with the voltage resistance of the supercapacitor cluster in the supercapacitor module and the insulation level of the equipment, the open circuit voltage V of the i-th supercapacitor energy storage branch is selected. SC_i and the equivalent capacitance C SC_i , reserve redundant super-capacity clusters and determine the number of super-capacity sub-modules connected in series in each super-capacity energy storage branch.

[0131] B3) In the active power balancing control module, the active power P output by the i-th over-capacity energy storage branch is SC_i and the DC bus voltage V dc The ratio of is taken as the DC current reference value I of the i-th super-capacity energy storage branch dc_refi ; The current of the i-th supercapacity energy storage branch I SC_i With the DC current reference value I dc_refi The difference between the two values ​​is obtained by the PI controller and then compared with the DC bus voltage V dc The voltage reference value of the ith super-capacity energy storage branch is obtained by summing up, and the voltage reference value of the ith super-capacity energy storage branch and the average voltage V of each super-capacity sub-module in the ith super-capacity energy storage branch are used to calculate the value of the super-capacity energy storage branch. SC_sm The ratio of determines the number of super-capacitor modules required to be put into the i-th super-capacitor energy storage branch. According to the number of super-capacitor modules put into use, the modulation link is used to generate a switching pulse to trigger the corresponding super-capacitor module in the i-th super-capacitor energy storage branch.

[0132] In order to improve the energy supply performance of the super-capacity energy storage branch and reduce the voltage fluctuation level of the MMC DC side, the present invention also proposes a super-capacity energy distribution and balancing configuration method for the networked HC-EVSC device, including:

[0133] Step 1: collecting the DC bus voltage as the rated voltage of each super-capacity energy storage branch;

[0134] In the embodiment, the DC bus voltage Vdc As the rated voltage of each super-capacity energy storage branch V SCN ;

[0135] Step 2: The excess energy balancing controller determines the maximum current of all excess energy storage branches based on the active power change and power recovery time of the MMC using the grid control strategy under the grid frequency step; and determines the number n of excess energy storage branches to be put into operation using the maximum current and the rated current of each excess energy storage branch.

[0136] In the embodiment, the maximum frequency step value f of the AC system connected to the MMC using the network control strategy is obtained. max In the scenario where three parallel MMCs all output rated active power and are not connected to an overcapacity energy storage branch, a simulation method is used to determine the maximum frequency step value f of the MMC using the grid control strategy. max The maximum value of the active power change under And the recovery time required for the active power to recover to the rated active power The maximum active power ΔP supported by all overcapacity energy storage branches max , support time ΔT max ;

[0137] In this embodiment, the active power supports the maximum value ΔP max and support time ΔT max is the upper limit of energy demand in the most extreme case; using the maximum active power supported by all overcapacity energy storage branches, support time and rated voltage, calculate the maximum current of all overcapacity energy storage branches to meet the following relationship:

[0138]

[0139] Where, I SCmax is the maximum current of all overcapacity energy storage branches;

[0140] Each supercapacitor module contains power devices and supercapacitor clusters; if I SCmax If it is not greater than the maximum current capacity of the power device, the number of super-capacity energy storage branches put into operation is 1; if I SCmax If the current is greater than the maximum current carrying capacity of the power device, multiple parallel super-capacity energy storage branches are put into use, and the number of super-capacity energy storage branches put into use is determined according to the maximum current of all super-capacity energy storage branches and the rated current of each super-capacity energy storage branch;

[0141] If multiple supercapacitor energy storage branches are installed in parallel, further consideration should be given to the differences in current flow and overload capacity between power devices and supercapacitor clusters from different manufacturers. The number of supercapacitor energy storage branches to be put into operation should be determined when the rated current of each supercapacitor energy storage branch satisfies the following relationship:

[0142]

[0143] In the formula, I SCN_i is the rated current of the ith super-capacity energy storage branch, which is determined according to the current-carrying capacity and overload capacity of power devices in different super-capacity energy storage branches, and n' is the number of super-capacity energy storage branches put into operation.

[0144] In step 3, the super-capacity energy balancing controller determines the total transmission power of all super-capacity energy storage branches and the energy coefficients of the super-capacity energy storage branches according to the active power shortage of the MMC adopting the network construction control strategy, and sends the total transmission power and the energy coefficients of the super-capacity energy storage branches to the corresponding super-capacity energy storage branch controllers respectively.

[0145] Specifically, the difference between the active power output by the MMC adopting the network construction control strategy and the active power reference value is the active power shortage; the super-capacity energy balancing controller takes the active power shortage as the total transmission power of all super-capacity energy storage branches, and satisfies the following relationship:

[0146] ΔP SC = P mmc -P mmc_ref

[0147] In the formula, ΔP SC is the total transmission power of all super-capacity energy storage branches, P mmc is the active power output by the MMC adopting the network construction control strategy, and P mmc_ref is the active power reference value of the MMC adopting the network construction control strategy.

[0148] The super-capacity energy balancing controller determines the energy coefficients of the super-capacity energy storage branches, including:

[0149] 1) Among all super-capacity energy storage branches, the energy coefficient of the super-capacity energy storage branch with the shortest electrical distance from the receiving end converter station is assigned the maximum value α', and in the embodiment, the value range of α' is [0.8, 1.0]; the energy coefficients of the remaining super-capacity energy storage branches are assigned equal values, all being α'', and satisfying α'+ (n-1)α'' = 1.

[0150] 2) The output power commands of the super-capacity energy storage branches are calculated by using the assignment of the energy coefficients of the super-capacity energy storage branches; the adjustment cost and adjustment time of each super-capacity energy storage branch are determined based on the output power commands of the super-capacity energy storage branches.

[0151] 3) each super-capacitor energy storage branch has a corresponding adjustment cost and adjustment time length when responding to the output power instruction, the adjustment cost represents the economy of the difference between the current output power actual value and the output power instruction of the branch, the adjustment time length is the time required for the branch to adjust from the current output power actual value to the output power instruction, which represents the technical performance of each super-capacitor sub-module in the branch, therefore, the comprehensive optimization of the adjustment cost and the adjustment time length of each super-capacitor energy storage branch, and the comprehensive optimization of the adjustment cost and the adjustment time length of all super-capacitor energy storage branches are taken as the objective function, the sum of the output power instructions of all super-capacitor energy storage branches meets the total transmission power of all super-capacitor energy storage branches as the constraint condition, and the energy coefficients of each super-capacitor energy storage branch are optimized through multiple iterations;

[0152] The objective function satisfies the following relationship:

[0153]

[0154] In the formula, F is the objective function, λ is the weight, which is taken as 0.5 in the embodiment, and a person skilled in the art can set different weights according to different economic or technical needs according to the actual engineering needs, C i , τ i are the adjustment cost and the adjustment time length of the i-th super-capacitor energy storage branch responding to the output power instruction, and C i = f(ΔP i ), τ i = f(ΔP i ), ΔP i is the difference between the current output power actual value and the output power instruction of the i-th super-capacitor energy storage branch, and f() represents the functional relationship;

[0155] The sum of the output power instructions of all super-capacitor energy storage branches meets the total transmission power of all super-capacitor energy storage branches as the constraint condition, which satisfies the following relationship:

[0156]

[0157] In the formula, is the output power instruction of the i-th super-capacitor energy storage branch, and ΔP SC is the total transmission power of all super-capacitor energy storage branches;

[0158] The optimized energy coefficients of each super-capacitor energy storage branch are α i , i = 1, 2, …, n, which satisfies

[0159] In the over-capacity energy equalization controller, the process of iteratively optimizing the energy coefficients according to the target function is actually a process of equalizing the energy coefficients between each branch except the over-capacity energy storage branch with the shortest electrical distance to the receiving end converter station. The maximum energy coefficient of the over-capacity energy storage branch with the shortest electrical distance to the receiving end converter station is the basis for improving the dynamic response speed, and the equalization of the remaining energy coefficients is the basis for achieving active power support.

[0160] Step 4, the over-capacity energy storage branch controller determines the output power instruction of the over-capacity energy storage branch according to the received total transmission power and energy coefficients; when the output power instruction of the over-capacity energy storage branch meets the maximum power support level constraint, the over-capacity energy storage branch controller dynamically adjusts the active power output by each over-capacity energy storage branch according to the output power instruction;

[0161] In the embodiment, during the transient state, the output power instruction of the over-capacity energy storage branch determined by the total transmission power and the energy coefficients should meet the maximum power support level constraint shown in the following relationship:

[0162]

[0163] In the formula, P is the output power instruction of the i-th over-capacity energy storage branch, P SC_imax P is the maximum power support level of the i-th over-capacity energy storage branch at the rated DC voltage of the receiving end converter station. The maximum power support level of each over-capacity energy storage branch is determined by dispersing the current-carrying capacity and overload capacity of the power devices in different over-capacity energy storage branches at the rated voltage;

[0164] When the output power instruction of the over-capacity energy storage branch does not meet the maximum power support level constraint, the active power output by the over-capacity energy storage branch is maintained at the maximum power support level, and returns to step 3 to re-optimize the energy coefficients of each over-capacity energy storage branch by the over-capacity energy equalization controller. Through feedback optimization of the energy coefficients, the problem of insufficient active power support caused by the lack of active power due to the failure of an over-capacity energy storage branch continuously outputting at the maximum power support level is avoided. Moreover, through feedback optimization of the energy coefficients, the goal of equalizing the energy of each over-capacity energy storage branch is ultimately achieved, the service life of each over-capacity energy storage branch is improved, and the standardized construction and operation and maintenance of each over-capacity energy storage branch are facilitated. Through steps 1 to 4, on the basis of achieving over-capacity energy dispersion and equalization configuration, the number of over-capacity sub-modules in series in each over-capacity energy storage branch is further determined, the utilization rate of over-capacity sub-modules in each over-capacity energy storage branch is improved, the redundant number of over-capacity sub-modules is reduced, and the construction cost is effectively controlled.

[0165] Step 5: Establish an equivalent circuit for each super-capacitor energy storage branch, the equivalent circuit including an equivalent capacitor and an equivalent internal resistance; based on the equivalent circuit, when the power released by the equivalent capacitor is not less than the sum of the power consumed by the equivalent internal resistance and the active power demand of the super-capacitor energy storage branch, determine the number of super-capacitor sub-modules connected in series in the super-capacitor energy storage branch according to the output power command, the open-circuit voltage, and the equivalent capacitance value;

[0166] Specifically, an equivalent circuit is established for each supercapacitor energy storage branch. The equivalent circuit is an ideal capacitor and an ideal resistor in series. The ideal capacitor value is the equivalent capacitance value C when all supercapacitor submodules in all supercapacitor energy storage branches are put into operation. SC_i The ideal resistance is the equivalent internal resistance R when all supercapacitor modules in all supercapacitor energy storage branches are put into operation. SC_i ;

[0167] The power consumed by the equivalent internal resistance of the i-th supercapacitor energy storage branch satisfies the following relationship:

[0168]

[0169] Where, P SCR_i is the power consumed by the equivalent internal resistance of the i-th supercapacitor energy storage branch, I SCN_i is the rated current of the i-th supercapacity energy storage branch, R SC_i is the equivalent internal resistance of the i-th supercapacity energy storage branch, ΔT max The support time of all overcapacity energy storage branches;

[0170] The power released by the equivalent capacitance of the i-th supercapacitor energy storage branch satisfies the following relationship:

[0171] P SCC_i ≥P SCN_i +P SCR_i

[0172] Where, P SCC_i is the power released by the equivalent capacitance of the i-th supercapacitor energy storage branch, P SCN_i is the active power demand of the i-th super-capacity energy storage branch based on the equivalent circuit, satisfying

[0173] On the basis that all the super-capacity energy storage branches are exactly the same, the equivalent circuits and their parameters are the same. Therefore, the active power demand of each super-capacity energy storage branch is a uniformly distributed value of the product of the maximum active power supported and the support time under extreme conditions, which is well matched with the result of the balanced configuration of the energy coefficients of each branch, and further promotes the realization of the goal of balanced energy configuration of each super-capacity energy storage branch.

[0174] According to step 4, under ideal conditions, the output power of the i-th excess capacity energy storage branch is equal to the output power instruction of the i-th excess capacity energy storage branch, satisfying the following relationship:

[0175]

[0176] Where, P SC_i is the active power output by the i-th overcapacity energy storage branch, α i is the energy coefficient of the i-th overcapacity energy storage branch, ΔP SC is the total transmission power of all super-capacity energy storage branches, V SC_i is the open circuit voltage of the i-th supercapacitor energy storage branch, V dc is the DC bus voltage of the receiving converter station, R SC_i is the equivalent internal resistance of the i-th supercapacity energy storage branch;

[0177] Therefore, when the power device overcurrent constraint, output power constraint, and energy constraint are satisfied simultaneously, the equivalent capacitance value in the supercapacitor energy storage branch satisfies the following relationship:

[0178]

[0179] Where V SC_i is the open circuit voltage of the i-th supercapacitor energy storage branch, V SCN is the rated voltage of each super-capacity energy storage branch, is the output power instruction of the i-th overcapacity energy storage branch;

[0180] Combined with the voltage resistance of the supercapacitor cluster in the supercapacitor module and the insulation level of the equipment, the open circuit voltage V of the i-th supercapacitor energy storage branch is selected. SC_i and the equivalent capacitance C SC_i , reserve redundant super-capacity clusters and determine the number of super-capacity sub-modules connected in series in each super-capacity energy storage branch.

[0181] Balanced control of active power output from each overcapacity energy storage branch, such as Figure 4 In the controller of the i-th super-capacity energy storage branch, the active power P output by the i-th super-capacity energy storage branch is SC_i and the DC bus voltage V dc The ratio of is taken as the DC current reference value I of the i-th super-capacity energy storage branch dc_refi ; The current of the i-th supercapacity energy storage branch I SC_i With the DC current reference value I dc_refi The difference between the two values ​​is obtained by the PI controller and then compared with the DC bus voltage V dc The voltage reference value of the ith super-capacity energy storage branch is obtained by summing up, and the voltage reference value of the ith super-capacity energy storage branch and the average voltage V of each super-capacity sub-module in the ith super-capacity energy storage branch are used to calculate the value of the super-capacity energy storage branch. SC_smThe ratio of determines the number of super-capacitor modules required to be put into the i-th super-capacitor energy storage branch. According to the number of super-capacitor modules required to be put into use, the modulation link is used to generate a switching pulse to trigger the corresponding super-capacitor module in the i-th super-capacitor energy storage branch.

[0182] Specifically, the design involves decentralized selection of supercapacitor parameters and balanced control of the active power output of each supercapacitor energy storage branch through the design of a supercapacitor energy balancing controller. Supercapacitor clusters and semiconductor devices produced by different manufacturers vary in their withstand voltage and overcurrent capabilities. Therefore, decentralized selection is employed in determining supercapacitor parameters to ensure safe and stable operation of branch equipment. Furthermore, to fully utilize the energy support capabilities of different supercapacitor branches, a supercapacitor energy balancing controller is employed to ensure reliable energy supply to these branches.

[0183] A simulation model of the HC-EVSC grid-connected flexible DC converter topology and its control method was constructed in PSCAD to verify the effectiveness of the proposed topology and control method. In the simulation model, one of the two MMC converter stations uses grid-connected control. The operating parameters of the single MMC converter station are shown in the following table.

[0184] Table 1 Parameters of the receiving-end converter of the flexible DC system

[0185] Converter rated operating power / MW 667 Valve side rated voltage / kV 182.6 Rated DC voltage / kV 400 Bridge arm inductance / mH 50 Rated angular frequency / rad / s 314 Number of flexible direct current MMC single bridge arm submodules 174 Existing submodule capacitance value / mF 18 Converter capacity / MVA 375 Rated ratio of commutation transformer 525 / 182.6 Rated impedance of commutation transformer 20％

[0186] For the design of the first part of the overcapacity energy balancing controller in the overcapacity configuration, the number of overcapacity branches in the simulation is considered to be 1 branch, and the branch energy coefficient α1 in the above-mentioned overcapacity energy balancing controller is 1. For the decentralized selection of overcapacity parameters in the second part of the overcapacity configuration, the detailed selection process is as follows:

[0187] 1) Select the rated voltage V of the supercapacitor energy storage branch SCN :V SCN and MMC DC bus voltage V dc Consistent, this example V SCN =400kV;

[0188] 2) Select the active support power △P of the overcapacity branch max and support time △T max :The maximum frequency step value of the AC system connected to the network control MMC converter station is selected as f max The frequency is selected as 0.5Hz. The established system simulation model is used to test the maximum active power variation △P of the MMC converter station under the condition of the maximum frequency step value of 0.5Hz in the AC system when the MMC system outputs rated power and there is no additional over-capacity branch. fmax It takes time △T for the active power to recover to the rated power. max is 0.5s; among them, the active simulation waveform of the MMC converter under the frequency step is as follows Figure 5 As shown;

[0189] 3) Select the number of overcapacity branches n: Based on the system active power and duration requirements, determine the number and maximum capacity of directly connected overcapacity energy storage branches that meet the overcurrent constraints of the energy storage branch devices. In this example, the number of branches is 1, and the total energy released is 600MJ.

[0190] 4) Select the number of overcapacity branches and configure them in detail. Select an overcapacity branch configuration that meets the device overcurrent, output power, and energy constraints. Reserve overcapacity redundant clusters to improve energy storage device reliability. Considering that the DC current of a single branch is no more than 3kA, select a 144V / 62.5F module with a single module internal resistance of 96mΩ. The total number of overcapacity valve submodules is 325.

[0191] The specific simulation process is as follows: the receiving-end single-valve group network control converter is operating at rated conditions 8 seconds ago. In the simulation, the AC system frequency is set to step from 50Hz to 49.5Hz at 8 seconds. The active power overload of the network control converter provides inertia support for the system. The overcapacity branch recognizes the power change at the receiving end and then outputs power, maintaining stable voltage and power on the DC side of the sending and receiving ends.

[0192] The present disclosure may be a system, method and / or computer program product. The computer program product may include a computer-readable storage medium carrying computer-readable program instructions for causing a processor to implement various aspects of the present disclosure.

[0193] A computer-readable storage medium can be a tangible device that can hold and store instructions for use by an instruction execution device. A computer-readable storage medium can be, for example, but not limited to, an electrical storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination thereof. More specific examples (a non-exhaustive list) of computer-readable storage media include: a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), a static random access memory (SRAM), a portable compact disc read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, a mechanical encoding device, such as a punch card or a raised structure in a groove on which instructions are stored, and any suitable combination thereof. As used herein, a computer-readable storage medium is not to be construed as a transient signal per se, such as a radio wave or other freely propagating electromagnetic wave, an electromagnetic wave propagating through a waveguide or other transmission medium (e.g., a light pulse through a fiber optic cable), or an electrical signal transmitted through an electrical wire.

[0194] The computer-readable program instructions described herein can be downloaded from a computer-readable storage medium to each computing / processing device, or downloaded to an external computer or external storage device via a network, such as the Internet, a local area network, a wide area network, and / or a wireless network. The network can include copper transmission cables, fiber optic transmission, wireless transmission, routers, firewalls, switches, gateway computers, and / or edge servers. The network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards the computer-readable program instructions to be stored in the computer-readable storage medium in each computing / processing device.

[0195] The computer program instructions for performing the operations of the present disclosure may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-dependent instructions, microcode, firmware instructions, state setting data, or source code or object code written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Smalltalk, C++, and conventional procedural programming languages ​​such as "C" language or similar programming languages. Computer-readable program instructions may be executed entirely on a user's computer, partially on a user's computer, as an independent software package, partially on a user's computer, partially on a remote computer, or entirely on a remote computer or server. In the case of a remote computer, the remote computer may be connected to the user's computer via any type of network, including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computer (e.g., utilizing an Internet service provider to connect via the Internet). In some embodiments, an electronic circuit, such as a programmable logic circuit, a field programmable gate array (FPGA), or a programmable logic array (PLA), may be personalized by utilizing the state information of the computer-readable program instructions. The electronic circuit may execute the computer-readable program instructions, thereby realizing various aspects of the present disclosure.

[0196] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the scope of protection of the claims of the present invention.

Claims

1. A networked HC-EVSC device, wherein the inverter side adopts a structure in which multiple parallel modular multilevel converters and a phase-commutation converter are cascaded, characterized in that: The device comprises: n parallel super-capacity energy storage branches configured on the inverter side, where n is a positive integer; one end of each super-capacity energy storage branch is connected to the positive electrode of the DC line, and the other end is connected to the ground electrode of the DC line; The device also includes: an overcapacity energy balancing controller, n overcapacity energy storage branch controllers; the overcapacity energy balancing controller includes: an overcapacity energy storage branch parameter configuration module and an energy balancing control module; the overcapacity energy storage branch parameter configuration module is used to determine the maximum current of all overcapacity energy storage branches based on the active power change and power recovery time of the modular multilevel converter adopting the network control strategy under the grid frequency step; and use the maximum current and the rated current of each overcapacity energy storage branch to determine the number of overcapacity energy storage branches connected in parallel; the energy balancing control module is used to determine the total transmission power of all overcapacity energy storage branches and the energy coefficient of each overcapacity energy storage branch based on the active power shortage of the modular multilevel converter adopting the network control strategy; and send the total transmission power and the energy coefficient of each overcapacity energy storage branch to the corresponding overcapacity energy storage branch controller respectively; The excess energy storage branch controller is used to determine the output power instruction of the excess energy storage branch based on the received total transmission power and energy coefficient; when the output power instruction of the excess energy storage branch meets the maximum power support level constraint, the excess energy storage branch controller adjusts the active power output of each excess energy storage branch according to the output power instruction.

2. The networked HC-EVSC device according to claim 1, characterized in that: Each supercapacitor energy storage branch includes multiple supercapacitor submodules connected in series; each supercapacitor submodule includes a power device and a supercapacitor cluster.

3. The networked HC-EVSC device according to claim 1, characterized in that: The super-capacity energy storage branch parameter configuration module includes: frequency step acquisition unit, simulation unit, branch current calculation unit, and branch quantity calculation unit; A frequency step acquisition unit, used to obtain a maximum frequency step value of an AC system connected to a modular multilevel converter adopting a network control strategy; a simulation unit for determining, by a simulation method, a maximum active power variation of the modular multilevel converters adopting a network control strategy at a maximum frequency step value and a power recovery time required for the active power to recover to the rated active power in a scenario where all modular multilevel converters output rated active power and are not connected to an overcapacity energy storage branch; A branch current calculation unit is configured to use the maximum active power variation output by the simulation unit as the maximum active power supported by all the over-capacity energy storage branches, and the power recovery time output by the simulation unit as the support time of all the over-capacity energy storage branches; and to calculate the maximum current of all the over-capacity energy storage branches using the maximum active power supported by all the over-capacity energy storage branches, the support time, and the rated voltage of each over-capacity energy storage branch; wherein the DC bus voltage is the rated voltage of each over-capacity energy storage branch; a branch quantity calculation unit, configured to: if the maximum current of all the excess energy storage branches is not greater than the maximum current carrying capacity of the power device, then the number of the excess energy storage branches is 1; if the maximum current of all the excess energy storage branches is greater than the maximum current carrying capacity of the power device, then determine the number of the excess energy storage branches connected in parallel based on the maximum current of all the excess energy storage branches and the rated current of each excess energy storage branch; wherein the rated current of each excess energy storage branch is determined based on the current carrying capacity and overload capacity of the power device in each excess energy storage branch.

4. The networked HC-EVSC device according to claim 3, characterized in that: The maximum current of all overcapacity energy storage branches satisfies the following relationship: Where, I SCmax is the maximum current of all overcapacity energy storage branches, ΔP max is the maximum active power supported by all overcapacity energy storage branches, ΔT max is the support time of all overcapacity energy storage branches, V SCN is the rated voltage of each super-capacity energy storage branch.

5. The networked HC-EVSC device according to claim 1, characterized in that: The energy balance control module includes: a total transmission power calculation unit; The total transmission power calculation unit is used to use the difference between the active power output by the modular multilevel converter adopting the network control strategy and the active power reference value as the active power shortage, and use the active power shortage as the total transmission power of all excess capacity energy storage branches.

6. The networked HC-EVSC device according to claim 5, characterized in that: The total transmission power of all super-capacity energy storage branches satisfies the following relationship: ΔP SC =P mmc -P mmc_ref Where ΔP SC is the total transmission power of all super-capacity energy storage branches, P mmc is the active power output by the MMC using the network control strategy, P mmc_ref It is the active power reference value output by the MMC using the network control strategy.

7. The networked HC-EVSC device according to claim 5, characterized in that: The energy balance control module further includes: an energy coefficient balance configuration unit; The energy coefficient balancing configuration unit is used to assign the maximum energy coefficient value to the excess energy storage branch with the shortest electrical distance to the receiving converter station among all excess energy storage branches, which is α′, and the value range of α′ is [0.8, 1.0]. The energy coefficients of the remaining excess energy storage branches are assigned the same value, which is α″, and satisfies α′+(n-1)α″=1. Utilizing the assigned values ​​of the energy coefficients of the respective excess energy storage branches, the output power instructions of the respective excess energy storage branches are calculated; based on the output power instructions of the respective excess energy storage branches, the regulation cost and regulation duration of the respective excess energy storage branches are determined; The objective function is to optimize the regulation cost and regulation time of each overcapacity energy storage branch and the regulation cost and regulation time of all overcapacity energy storage branches. The constraint condition is that the sum of the output power instructions of all overcapacity energy storage branches meets the total transmission power of all overcapacity energy storage branches. The energy coefficient of each overcapacity energy storage branch is optimized through multiple iterations. The energy coefficient of each overcapacity energy storage branch after optimization is α i , i=1,2,…,n, satisfying 8. The networked HC-EVSC device according to claim 7, characterized in that: The objective function satisfies the following relationship: In the formula, F is the objective function, λ is the weight, C i , τ i are the adjustment cost and adjustment time of the i-th overcapacity energy storage branch in response to the output power instruction, and C i =f(ΔP i ), τ i =f(ΔP i ), ΔP i is the difference between the actual output power value of the i-th over-capacity energy storage branch and the output power command, and f() represents the functional relationship; The sum of the output power instructions of all excess energy storage branches satisfies the total transmission power of all excess energy storage branches as a constraint condition, and satisfies the following relationship: Where, is the output power instruction of the i-th overcapacity energy storage branch, ΔP SC is the total transmission power of all super-capacity energy storage branches.

9. The networked HC-EVSC device according to claim 7, characterized in that: The super-capacity energy storage branch controller includes: an output power instruction generation module; An output power instruction generation module is used to determine the output power instruction of the excess energy storage branch based on the received total transmission power and energy coefficient; when the output power instruction of the excess energy storage branch meets the maximum power support level constraint, the excess energy storage branch controller adjusts the active power output of each excess energy storage branch according to the output power instruction; When the output power instruction of the excess energy storage branch does not meet the maximum power support level constraint, the active power output by the excess energy storage branch is maintained at the maximum power support level, and a signal is sent to the excess energy balancing controller to re-optimize the energy coefficient of each excess energy storage branch.

10. The networked HC-EVSC device according to claim 9, characterized in that: The output power instruction of the overcapacity energy storage branch determined by the output power instruction generation module should meet the maximum power support level constraint shown in the following relationship: Where, is the output power instruction of the i-th super-capacity energy storage branch, P SC_imax is the maximum power support level of the i-th over-capacity energy storage branch under the rated DC voltage of the receiving-end converter station. The maximum power support level of each over-capacity energy storage branch is determined according to the current-carrying capacity and overload capacity of the power devices in each over-capacity energy storage branch under the rated voltage.

11. The networked HC-EVSC device according to claim 9, characterized in that: The super-capacity energy storage branch controller further includes: a super-capacity sub-module parameter configuration module; The super-capacitor module parameter configuration module is used to establish an equivalent circuit of the super-capacitor energy storage branch before adjusting the active power output of each super-capacitor energy storage branch according to the output power instruction. The equivalent circuit includes an equivalent capacitor and an equivalent internal resistance. Based on the equivalent circuit, when the power released by the equivalent capacitor is not less than the sum of the power consumed by the equivalent internal resistance and the active power demand of the super-capacitor energy storage branch, the number of super-capacitor sub-modules connected in series in the super-capacitor energy storage branch is determined according to the output power instruction, the open-circuit voltage and the equivalent capacitance value.

12. The networked HC-EVSC device according to claim 11, characterized in that: The supercapacitor module parameter configuration module includes: an equivalent circuit establishment unit; The equivalent circuit establishment unit is used to establish the equivalent circuit of each super-capacitor energy storage branch. The equivalent circuit is an ideal capacitor and an ideal resistor in series. The ideal capacitor value is the equivalent capacitance value C when all super-capacitor sub-modules in all super-capacitor energy storage branches are put into operation. SC_i The ideal resistance is the equivalent internal resistance R when all supercapacitor modules in all supercapacitor energy storage branches are put into operation. SC_i ; The power consumed by the equivalent internal resistance of the i-th supercapacitor energy storage branch satisfies the following relationship: Where, P SCR_i is the power consumed by the equivalent internal resistance of the i-th supercapacitor energy storage branch, I SCN_i is the rated current of the i-th supercapacity energy storage branch, R SC_i is the equivalent internal resistance of the i-th supercapacity energy storage branch, ΔT max The support time of all overcapacity energy storage branches; The power released by the equivalent capacitance of the i-th supercapacitor energy storage branch satisfies the following relationship: P SCC_i ≥P SCN_i +P SCR_i Where, P SCC_i is the power released by the equivalent capacitance of the i-th supercapacitor energy storage branch, P SCN_i is the active power demand of the i-th super-capacity energy storage branch based on the equivalent circuit, satisfying ΔP max It is the maximum active power supported by all overcapacity energy storage branches.

13. The networked HC-EVSC device according to claim 12, characterized in that: The super-capacitor module parameter configuration module further includes: a super-capacitor module quantity calculation unit; In the super-capacitor module quantity calculation unit, the equivalent capacitance value in the super-capacitor energy storage branch is determined to satisfy the following relationship: Where V SC_i is the open circuit voltage of the i-th supercapacitor energy storage branch, V SCN is the rated voltage of each super-capacity energy storage branch, is the output power instruction of the i-th overcapacity energy storage branch; Combined with the voltage resistance of the supercapacitor cluster in the supercapacitor module and the insulation level of the equipment, the open circuit voltage V of the i-th supercapacitor energy storage branch is selected. SC_i and the equivalent capacitance C SC_i , reserve redundant super-capacity clusters and determine the number of super-capacity sub-modules connected in series in each super-capacity energy storage branch.

14. The networked HC-EVSC device according to claim 9, characterized in that: The super-capacity energy storage branch controller also includes: an active power balancing control module; In the active power balancing control module, the active power P output by the i-th overcapacity energy storage branch is SC_i and the DC bus voltage V dc The ratio of is taken as the DC current reference value I of the i-th super-capacity energy storage branch dc_refi ; The current of the i-th supercapacity energy storage branch I SC_i With the DC current reference value I dc_refi The difference between the two values ​​is obtained by the PI controller and then compared with the DC bus voltage V dc The voltage reference value of the ith super-capacity energy storage branch is obtained by summing up, and the voltage reference value of the ith super-capacity energy storage branch and the average voltage V of each super-capacity sub-module in the ith super-capacity energy storage branch are used to calculate the value of the super-capacity energy storage branch. SC_sm The ratio of determines the number of super-capacitor modules required to be put into the i-th super-capacitor energy storage branch. According to the number of super-capacitor modules put into use, the modulation link is used to generate a switching pulse to trigger the corresponding super-capacitor module in the i-th super-capacitor energy storage branch.

15. A method for distributing and balancing supercapacity energy in a networked HC-EVSC device, applicable to the device according to any one of claims 1 to 14, characterized in that: include: Collect the DC bus voltage as the rated voltage of each super-capacity energy storage branch; An overcapacity energy balancing controller includes: an overcapacity energy storage branch parameter configuration module and an energy balancing control module; the overcapacity energy storage branch parameter configuration module is used to determine the maximum current of all overcapacity energy storage branches based on the active power change and power recovery time of the modular multilevel converter adopting the network control strategy under the grid frequency step; and the number of overcapacity energy storage branches connected in parallel is determined by using the maximum current and the rated current of each overcapacity energy storage branch; the energy balancing control module is used to determine the total transmission power of all overcapacity energy storage branches and the energy coefficient of each overcapacity energy storage branch based on the active power shortage of the modular multilevel converter adopting the network control strategy; and the total transmission power and the energy coefficient of each overcapacity energy storage branch are respectively sent to the corresponding overcapacity energy storage branch controller; The excess energy storage branch controller determines the output power instruction of the excess energy storage branch based on the received total transmission power and energy coefficient. When the output power instruction of the excess energy storage branch meets the maximum power support level constraint, the excess energy storage branch controller dynamically adjusts the active power output of each excess energy storage branch according to the output power instruction. An equivalent circuit is established for each super-capacitive energy storage branch, which includes an equivalent capacitor and an equivalent internal resistance. Based on the equivalent circuit, when the power released by the equivalent capacitor is not less than the sum of the power consumed by the equivalent internal resistance and the active power demand of the super-capacitive energy storage branch, the number of super-capacitive sub-modules connected in series in the super-capacitive energy storage branch is determined according to the output power command, open-circuit voltage, and equivalent capacitance value.

16. A terminal comprising a processor and a storage medium; characterized in that: The storage medium is used to store instructions; The processor is configured to operate according to the instructions to execute the steps of the method of claim 15 .

17. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the steps of the method according to claim 15 are implemented.

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