Method and device for suppressing secondary ripple current of angular medium-voltage direct-hung chain energy storage

Abstract

The application discloses a kind of angle type medium voltage straight hanging chain energy storage secondary ripple current suppression method and device, method includes: obtaining three-phase power grid voltage amplitude and three-phase power grid voltage phase;According to three-phase power grid voltage amplitude and preset active and reactive power instruction, obtain three-phase active and reactive current instruction amplitude;According to the state of charge of each submodule and three-phase power grid voltage amplitude, obtain zero sequence current instruction and the additional equalization voltage of each submodule;According to three-phase active and reactive current instruction amplitude, three-phase power grid voltage phase and zero sequence current instruction, obtain three-phase current instruction and third harmonic current instruction;Three harmonic current instruction is added with three-phase current instruction, and after subtracting each phase sampling current, it is sent into quasi-proportional resonant controller, obtains the first data of each phase;The first data in each phase is added with additional equalization voltage, and the second data of each submodule is obtained;According to the second data, drive each submodule after carrier phase-shift modulation.

Description

Technical Field

[0001] This invention relates to the field of battery energy storage conversion technology, and in particular to a method and apparatus for suppressing secondary ripple current in angle-type medium-voltage direct-connected chain energy storage. Background Technology

[0002] Faced with the energy crisis, environmental pollution, and climate change, the traditional energy structure can no longer meet the needs of sustainable development, and a green energy transition is imminent. Wind power and photovoltaic power have developed rapidly due to their wide range and large scale, but their volatility and randomness pose challenges to power system dispatch and safe and stable operation. Compared with traditional power systems, new power systems have characteristics such as low short-circuit ratio and insufficient inertia, which increases the risk of unit cascading disconnection.

[0003] Energy storage technology, with its peak-valley regulation and inertia support functions, has become a key technology for building new power systems. Battery energy storage systems need to develop towards larger single-unit capacities to meet the grid stability requirements of new energy power generation and power electronic equipment grid connection. A battery energy storage system consists of batteries, a battery management system (BESS), a power conversion system (PCS), and a monitoring and management system. The PCS, as the interface between the energy storage battery and the grid, is crucial in determining the performance of the BESS. Medium-voltage direct-connected chain energy storage systems have broad prospects due to their advantages such as transformerless grid connection, modular structure, and large single-unit capacity. However, in delta-type medium-voltage direct-connected chain energy storage PCS systems, each phase is composed of multiple cascaded sub-modules. Due to the inherent power characteristics of single-phase inverters, the battery current of the sub-modules contains a large amount of secondary ripple components. These secondary ripple components not only adversely affect battery capacity and state monitoring but also reduce system efficiency and shorten battery life. Currently, most mainstream ripple current suppression methods rely on external hardware circuits, significantly increasing the system's size, cost, and structural and control complexity.

[0004] Therefore, a new technical solution is urgently needed to address the technical problem of actively suppressing the secondary ripple current in a diagonal medium-voltage direct-connected chain energy storage system. Summary of the Invention

[0005] This invention provides a method and apparatus for suppressing secondary ripple current in a corner-type medium-voltage direct-chain energy storage system, which solves the technical problem of how to actively suppress the secondary ripple current in a corner-type medium-voltage direct-chain energy storage system.

[0006] To achieve the above objectives, the present invention provides a method for suppressing secondary ripple current in a delta-type medium-voltage direct-connected chain energy storage system, characterized by comprising:

[0007] The three-phase grid voltage amplitude and phase are obtained; the three-phase active and reactive current command amplitudes are obtained based on the three-phase grid voltage amplitude and preset active and reactive power commands; the zero-sequence current command and the additional equalization voltage of each submodule are obtained based on the state of charge of each submodule and the three-phase grid voltage amplitude; the three-phase current command and the third harmonic current command are obtained based on the three-phase active and reactive current command amplitudes, the three-phase grid voltage phase and the zero-sequence current command.

[0008] The third harmonic current command is added to the three-phase current command and the sampled current of each phase is subtracted before being sent to the quasi-proportional resonant controller to obtain the first data of each phase; the first data of each phase is added to the additional equalization voltage to obtain the second data of each submodule; and each submodule is driven after carrier phase shift modulation is performed based on the second data.

[0009] Preferably, the zero-sequence current command and the additional equalization voltage of each submodule are obtained based on the state of charge of each submodule and the three-phase grid voltage amplitude, including:

[0010] Obtain the state of charge (SOC) of each submodule's energy storage battery, and derive the SOC of each phase based on the SOC. Average state of charge of three-phase energy storage batteries and the deviation of each phase-linked energy storage battery ; .

[0011] Based on the deviation of each phase link energy storage battery and three-phase power grid voltage amplitude Receive zero-sequence current command Component amplitude and ,include:

[0012] ;

[0013] in, The deviation adjustment coefficient determines the speed of interphase SOC equalization. for Deviation in the ab-phase linkage energy storage battery; for Deviation in the bc phase linkage energy storage battery.

[0014] According to the zero-sequence current command Component amplitude and and the voltage phase of the three-phase power grid ab phase in Receive zero-sequence current command :

[0015] ;

[0016] The additional equalization voltage for each submodule includes:

[0017] ;

[0018] in, Indicates an additional equalizing voltage; This represents the adjustment coefficient for intraphase SOC equalization, used to adjust the equalization speed. Indicates the SOC deviation of the submodule within the phase; This represents the sampled current of each phase; and This indicates the command amplitude of the three-phase active and reactive currents; j represents the j-th submodule within a phase. This represents the total number of submodules within a phase.

[0019] Preferably, the three-phase current command and the third harmonic current command are obtained based on the amplitude of the three-phase active and reactive current commands, the phase of the three-phase grid voltage, and the zero-sequence current command, including:

[0020] Based on the three-phase active and reactive current command amplitudes and Three-phase power grid voltage phase and zero-sequence current command Receive three-phase current command :

[0021] ;

[0022] The third harmonic current command is obtained based on the three-phase current command, the amplitude of the three-phase active and reactive current commands, the phase of the three-phase grid voltage, and the amplitude of the pq component of the zero-sequence current command.

[0023] Preferably, the third harmonic current command is obtained based on the three-phase current command, the amplitude of the three-phase active and reactive current commands, the phase of the three-phase grid voltage, and the amplitude of the pq component of the zero-sequence current command, including:

[0024] According to the three-phase current command and three-phase grid voltage Obtain the system power factor angle ,include:

[0025] Three-phase current command The Park transformation is performed, with the Park transformation rotating synchronously at an angle equal to the three-phase grid voltage. ab phase in Receive three-phase current command Component amplitude and :

[0026] ;

[0027] According to the three-phase current command Component amplitude and Obtain the system power factor angle ,include:

[0028] ;

[0029] According to the zero-sequence current command Component amplitude and and the command amplitude of three-phase active and reactive currents and The current amplitude and phase are calculated to obtain the three-phase current amplitude. Phase with three-phase current :

[0030] ;

[0031] ;

[0032] According to the system power factor angle Three-phase current amplitude Phase of three-phase current conduct Value calculation to obtain the expected value Value and Expectation The value corresponds to the phase current amplitude. ;in Value is the amplitude of the third harmonic current. With the amplitude of the fundamental frequency phase current The ratio.

[0033] According to the system power factor angle ,expect Value and current amplitude Receive third harmonic current command ,include:

[0034] ;

[0035] Preferred, to be carried out Value calculations include:

[0036] When the system power factor angle When it is 0:

[0037] like ,Pick phase value =1, where for The maximum allowable value of the phase current; if Solving the first equation yields phase value The first equation includes:

[0038] ;

[0039] in, This indicates the ratio of the phase current amplitude before and after the injection of third harmonic current in each phase.

[0040] When the system power factor angle When not equal to 0:

[0041] According to the angle of each phase Combined with system power factor Obtain the phase correction value of the three-phase current under asymmetrical operating conditions. and the phase correction value of the three-phase current The three-phase current phase transition value is obtained by performing interval transformation. :

[0042] ;

[0043] ;

[0044] The fitting coefficient is obtained through the formula for calculating the fitting coefficient. , , , , Solving the second equation yields... , and Three solutions, and take phase value The second equation includes:

[0045] ;

[0046] In the calculation phase value Right now , and Then, take the expected value. Value and get what you expect. The value corresponds to the phase current amplitude. .

[0047] The fitting coefficients are obtained through the formula for calculating the fitting coefficients, including:

[0048] when hour:

[0049] ;

[0050] when hour:

[0051] ;

[0052] The present invention also provides a secondary ripple current suppression device for angle-type medium-voltage direct-connected chain energy storage, used in the method of the present invention, the device comprising a first module, a second module and a third module.

[0053] The first module is used to obtain the voltage amplitude and phase of the three-phase power grid; and to obtain the voltage amplitude of the three-phase active and reactive current commands based on the voltage amplitude of the three-phase power grid and the preset active and reactive power commands.

[0054] The second module is used to obtain the zero-sequence current command and the additional equalization voltage of each sub-module based on the state of charge of each sub-module and the amplitude of the three-phase grid voltage; and to obtain the three-phase current command and the third harmonic current command based on the amplitude of the three-phase active and reactive current commands, the phase of the three-phase grid voltage and the zero-sequence current command.

[0055] The third module is used to add the third harmonic current command and the three-phase current command, subtract the sampled current of each phase, and then send the result to the quasi-proportional resonant controller to obtain the first data of each phase; add the first data of each phase to the additional equalization voltage to obtain the second data of each submodule; and drive each submodule after performing carrier phase shift modulation based on the second data.

[0056] The present invention has the following beneficial effects:

[0057] The present invention discloses a method for suppressing second-order ripple current in a delta-type medium-voltage direct-connected chain energy storage system. This method injects a third-harmonic current with the same amplitude and phase into the AC side current. For a delta structure, this does not affect the final current output of the system. The third-harmonic current, after being modulated by an H-bridge converter, generates second and fourth-order components on the DC side. If the injected third-harmonic current meets optimal conditions, the second-order component generated by the latter can cancel out the original second-order component, thereby suppressing the second-order ripple component on the DC side. The method prioritizes ensuring the three-phase external power output and ensures that the phase current after injecting the third-harmonic current meets the current-limiting constraint. It proposes a method for solving the optimal third-harmonic current under unity power factor conditions, and also proposes a method for solving the optimal third-harmonic current through curve fitting under non-unity power factor conditions. This method eliminates the need for additional hardware filtering circuits and can effectively suppress the second-order ripple current under both unity and non-unity power factor conditions, while ensuring that the current does not exceed the maximum allowable value. This significantly reduces system size, cost, and control complexity, and improves system operating efficiency and the lifespan of the energy storage unit. This invention can actively suppress secondary ripple current at the source, reduce battery ripple current, and improve system efficiency and battery life.

[0058] The secondary ripple current suppression device for angle-type medium-voltage direct-connected chain energy storage of the present invention, when used in the method of the present invention, has the same beneficial effects as the method of the present invention.

[0059] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. The invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0060] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0061] Figure 1 This is a schematic diagram of the angled medium-pressure direct-connected chain energy storage system according to a preferred embodiment of the present invention.

[0062] Figure 2 This is a schematic diagram of the method flow of a preferred embodiment of the present invention.

[0063] Figure 3 This is a method control block diagram of a preferred embodiment of the present invention.

[0064] Figure 4 This is a block diagram of the control for solving the third harmonic current command according to a preferred embodiment of the present invention.

[0065] Figure 5 This is a preferred embodiment of the present invention. k Schematic diagram of value calculation process.

[0066] Figure 6 This is a simulated waveform of the battery current before and after the addition of the ripple suppression strategy of this invention when the angled medium-voltage direct-connected chain energy storage system of this invention is operating under half-load active power.

[0067] Figure 7 The simulation waveform of the system output current before and after adding the ripple suppression strategy of the present invention when the angle-type medium-voltage direct-connected chain energy storage system of the present invention is operating under half-load active power.

[0068] Figure 8 The image shows the simulated battery current waveforms before and after incorporating the ripple suppression strategy of this invention when the angled medium-voltage direct-connected chain energy storage system of this invention is operating at full active load.

[0069] Figure 9 The simulation waveform of the system output current before and after adding the ripple suppression strategy of the present invention when the angle-type medium-voltage direct-connected chain energy storage system of the preferred embodiment of the present invention is operating at full active load.

[0070] Figure 10 This is a simulation waveform diagram of the dynamic adjustment verification of the ripple current suppression strategy of the present invention in a preferred embodiment of the angle-type medium-voltage direct-connected chain energy storage system operating at unity power factor.

[0071] Figure 11 The image shows the simulated battery current waveforms before and after incorporating the ripple suppression strategy of this invention when the angled medium-voltage direct-connected chain energy storage system of this invention is operating under reactive half-load conditions.

[0072] Figure 12 The simulation waveform of the system output current before and after adding the ripple suppression strategy of the present invention is shown in the preferred embodiment of the angle-type medium-voltage direct-connected chain energy storage system when it is operating under reactive half-load.

[0073] Figure 13 This is a simulation waveform diagram of the dynamic adjustment verification of the ripple current suppression strategy of the present invention in a preferred embodiment of the angle-type medium-voltage direct-connected chain energy storage system operating under non-unity power factor.

[0074] Figure 14 This is a simulation waveform diagram of secondary ripple current suppression in a corner-type medium-voltage direct-connected chain energy storage system of the preferred embodiment of the present invention when operating in phase-to-phase SOC equalization. Detailed Implementation

[0075] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings, but the present invention can be implemented in many different ways as defined and covered by the claims.

[0076] See Figure 1 The angle-type medium-voltage direct-connected chain energy storage system of the present invention includes an AC filter inductor. The system includes fuses, contactors, and 3N H-bridge power conversion units. Each H-bridge power conversion unit, a submodule of this invention, comprises a DC-side inductor, a storage battery, a full-bridge converter, and a DC-side capacitor. The positive terminal of the full-bridge converter's DC side is connected in series with the DC-side inductor and the storage battery, and then connected to the negative terminal of the full-bridge converter's DC side. The DC-side capacitor is connected in parallel across the two terminals of the full-bridge converter's DC side. N H-bridge power conversion units in each phase are cascaded on the AC side to form a PCS link, and each phase PCS link is connected sequentially in a delta configuration. Each phase PCS link is connected via an AC filter inductor. The fuses and contactors are connected to the AC power grid.

[0077] exist Figure 1 In this context, SMN represents the Nth submodule; Let x be the line voltage of the AC power grid, and let x = ab, bc, ca, representing phases ab, bc, and ca, respectively.

[0078] See Figures 2 to 3 In a preferred embodiment of the present invention, a method for suppressing secondary ripple current in angle-type medium-voltage direct-connected chain energy storage is provided, comprising:

[0079] S1. Obtain the three-phase grid voltage amplitude and the three-phase grid voltage phase; obtain the three-phase active and reactive current command amplitudes based on the three-phase grid voltage amplitude and the preset active and reactive power commands.

[0080] In a preferred embodiment of the present invention, obtaining the three-phase grid voltage amplitude and the three-phase grid voltage phase includes:

[0081] Obtain the line voltage of the AC power grid See also Figure 3 The single-phase phase-locked loop section in the middle is based on the line voltage. The three-phase power grid voltage amplitude is obtained through a single-phase phase-locked loop (PLL). Phase of three-phase power grid voltage ; .

[0082] See Figure 3 In the phase-separated current loop section of the present invention, in a preferred embodiment, the three-phase active and reactive current command amplitudes are obtained based on the three-phase grid voltage amplitude and preset active and reactive power commands, including:

[0083] ;

[0084] in, and These represent the preset active and reactive power commands, respectively. and These represent the command amplitudes of the three-phase active and reactive currents, respectively.

[0085] S2. Based on the state of charge of each submodule and the amplitude of the three-phase grid voltage, obtain the zero-sequence current command and the additional equalization voltage of each submodule; based on the amplitude of the three-phase active and reactive current commands, the phase of the three-phase grid voltage and the zero-sequence current command, obtain the three-phase current command and the third harmonic current command.

[0086] See Figure 3 In the SOC balancing calculation section of this invention, in a preferred embodiment, the zero-sequence current command and the additional balancing voltage of each submodule are obtained based on the state of charge of each submodule and the three-phase grid voltage amplitude, including:

[0087] Obtain the state of charge (SOC) of each submodule's energy storage battery, and derive the SOC of each phase based on the SOC. Average state of charge of three-phase energy storage batteries and the deviation of each phase-linked energy storage battery ; ,include:

[0088] ;

[0089] in, for Xiangdi The state of charge of each sub-module battery pack.

[0090] Based on the deviation of each phase link energy storage battery and three-phase power grid voltage amplitude Receive zero-sequence current command Component amplitude and ,include:

[0091] ;

[0092] in, The deviation adjustment coefficient determines the speed of interphase SOC equalization. for Deviation in the ab-phase linkage energy storage battery; for Deviation in the bc phase linkage energy storage battery.

[0093] According to the zero-sequence current command Component amplitude and and the voltage phase of the three-phase power grid ab phase in The zero-sequence current command is obtained to achieve interphase SOC equalization. :

[0094] ;

[0095] In a preferred embodiment of the present invention, the zero-sequence current command Alternatively, the phase of another phase can be used as a reference for construction. If the phase of another phase is selected for construction, the subsequent related calculations can be adaptively modified.

[0096] The additional equalization voltage for each submodule includes:

[0097] ;

[0098] ;

[0099] in, Indicates an additional equalizing voltage; This represents the adjustment coefficient for intraphase SOC equalization, used to adjust the equalization speed. Indicates the SOC deviation of the submodule within the phase; This represents the sampled current of each phase; and This indicates the command amplitude of the three-phase active and reactive currents; j represents the j-th submodule within a phase. This represents the total number of submodules within a phase.

[0100] In a preferred embodiment of the present invention, see [reference needed]. Figure 4 Based on the amplitudes of the three-phase active and reactive current commands, the phases of the three-phase grid voltage, and the zero-sequence current command, the three-phase current command and the third harmonic current command are obtained, including:

[0101] Based on the three-phase active and reactive current command amplitudes and Three-phase power grid voltage phase and zero-sequence current command Receive three-phase current command :

[0102] ;

[0103] The third harmonic current command is obtained based on the three-phase current command, the amplitude of the three-phase active and reactive current commands, the phase of the three-phase grid voltage, and the amplitude of the pq component of the zero-sequence current command. Specifically, it includes:

[0104] According to the three-phase current command and three-phase grid voltage Obtain the system power factor angle ,include:

[0105] Three-phase current command The Park transformation is performed, with the Park transformation rotating synchronously at an angle equal to the three-phase grid voltage. ab phase in Receive three-phase current command Component amplitude and :

[0106] ;

[0107] According to the three-phase current command Component amplitude and Obtain the system power factor angle ,include:

[0108] ;

[0109] In a preferred embodiment of the present invention, since the zero-sequence current command is phased with the ab line voltage... Construction based on a single standard cannot be achieved through a unified formula; therefore, it is based on the zero-sequence current command. Component amplitude and and the command amplitude of three-phase active and reactive currents and The current amplitude and phase are calculated to obtain the three-phase current amplitude. Phase with three-phase current :

[0110] ;

[0111] ;

[0112] According to the system power factor angle Three-phase current amplitude Phase of three-phase current conduct Value calculation to obtain the expected value Value and Expectation The value corresponds to the phase current amplitude. ;in Value is the amplitude of the third harmonic current. With the amplitude of the fundamental frequency phase current The ratio.

[0113] According to the system power factor angle ,expect Value and current amplitude The command to inject the third harmonic current to suppress the second harmonic current is obtained. ,include:

[0114] ;

[0115] In a preferred embodiment of the present invention, see [reference needed]. Figure 5 ,conduct Value calculations include:

[0116] When the system power factor angle When it is 0:

[0117] like ,Pick phase value =1, where for The maximum allowable value of the phase current; if Solving the first equation yields phase value The first equation includes:

[0118] ;

[0119] in, This indicates the ratio of the phase current amplitude before and after the injection of third harmonic current in each phase.

[0120] When the system power factor angle When not equal to 0:

[0121] Considering that the system may experience three-phase current asymmetry during actual operation, in order to unify the calculation of the second equation, based on the angle of each phase... Combined with system power factor Obtain the phase correction value of the three-phase current under asymmetrical operating conditions. Because the phase difference is of The second equation expression corresponding to the value is the same, and the fitting coefficient is... , , , , exist Belongs to (0, The interval is about Symmetry, correcting the phase of the three-phase current The three-phase current phase transition value is obtained by performing interval transformation. :

[0122] ;

[0123] ;

[0124] The fitting coefficient is obtained through the formula for calculating the fitting coefficient. , , , , Solving the second equation yields... , and Three solutions, and take phase value The second equation includes:

[0125] ;

[0126] In the calculation phase value Right now , and Then, take the expected value. Value and get what you expect. The value corresponds to the phase current amplitude. .

[0127] In a preferred embodiment of the present invention, the fitting coefficients are obtained through the fitting coefficient calculation formula, including:

[0128] when hour:

[0129] ;

[0130] when hour:

[0131] ;

[0132] S3. The third harmonic current command is added to the three-phase current command, and the sampled current of each phase is subtracted before being sent to the quasi-proportional resonant controller to obtain the first data for each phase. The first data of each phase is added to the additional equalization voltage to obtain the second data for each submodule. Based on the second data, carrier phase-shift modulation is performed to drive each submodule. See details. Figure 3 The phase current loop section in the middle.

[0133] Carrier phase-shift modulation is performed based on the second data of each submodule to obtain the drive signal of the switching transistor in each submodule. The submodule is then driven according to the drive signal to achieve secondary ripple current suppression.

[0134] In a quasi-proportional resonant controller, the transfer function includes:

[0135] ;

[0136] in The fundamental angular frequency, For quasi-PR controller gain parameters, , These are the fundamental frequency and third harmonic resonant parameters, respectively. , These are the fundamental frequency and the third harmonic damping frequency, respectively. The variable in the complex frequency domain is the result of the Laplace transform of the time-domain input signal.

[0137] The present invention discloses a method for suppressing second-order ripple current in a delta-type medium-voltage direct-connected chain energy storage system. This method injects a third-harmonic current with the same amplitude and phase into the AC side current. For a delta structure, this does not affect the final current output of the system. The third-harmonic current, after being modulated by an H-bridge converter, generates second and fourth-order components on the DC side. If the injected third-harmonic current meets optimal conditions, the second-order component generated by the latter can cancel out the original second-order component, thereby suppressing the second-order ripple component on the DC side. The method prioritizes ensuring the three-phase external power output and ensures that the phase current after injecting the third-harmonic current meets the current-limiting constraint. It proposes a method for solving the optimal third-harmonic current under unity power factor conditions, and also proposes a method for solving the optimal third-harmonic current through curve fitting under non-unity power factor conditions. This method eliminates the need for additional hardware filtering circuits and can effectively suppress the second-order ripple current under both unity and non-unity power factor conditions, while ensuring that the current does not exceed the maximum allowable value. This significantly reduces system size, cost, and control complexity, and improves system operating efficiency and the lifespan of the energy storage unit. This invention can actively suppress secondary ripple current at the source, reduce battery ripple current, and improve system efficiency and battery life.

[0138] In a preferred embodiment of the present invention, injecting a third harmonic current on the AC side introduces a higher-frequency fourth component on the DC side. However, the LC filter attenuates the fourth component significantly more effectively than the second component, thus effectively suppressing the fourth ripple current component flowing through the battery branch. Therefore, overall, the ripple current content of the battery branch is significantly reduced after injecting the third harmonic current. From another perspective, under the same ripple current requirement, injecting the third harmonic current allows for a higher cutoff frequency of the LC filter required on the DC side, thereby reducing the filter's size, weight, and cost.

[0139] Compared with existing technologies, this invention achieves active suppression of the second-order ripple current on the DC side of the angle-type medium-voltage direct-connected chain energy storage system through third-order harmonic current injection, reducing ripple current at the source. It proposes a dynamic solution method for the third-order harmonic current under unity power factor and non-unity power factor conditions, ensuring that the second-order ripple current can be effectively suppressed under different operating conditions, while ensuring that the phase current does not exceed the current limit value. Compared with traditional passive filtering methods, it significantly reduces the system's size, cost and control complexity.

[0140] In a preferred embodiment of the present invention, a secondary ripple current suppression device for angle-type medium-voltage direct-connected chain energy storage is also provided for use in the method of the present invention. The device includes a first module, a second module, and a third module.

[0141] The first module is used to obtain the voltage amplitude and phase of the three-phase power grid; and to obtain the voltage amplitude of the three-phase active and reactive current commands based on the voltage amplitude of the three-phase power grid and the preset active and reactive power commands.

[0142] The second module is used to obtain the zero-sequence current command and the additional equalization voltage of each sub-module based on the state of charge of each sub-module and the amplitude of the three-phase grid voltage; and to obtain the three-phase current command and the third harmonic current command based on the amplitude of the three-phase active and reactive current commands, the phase of the three-phase grid voltage and the zero-sequence current command.

[0143] The third module is used to add the third harmonic current command and the three-phase current command, subtract the sampled current of each phase, and then send the result to the quasi-proportional resonant controller to obtain the first data of each phase; add the first data of each phase to the additional equalization voltage to obtain the second data of each submodule; and drive each submodule after performing carrier phase shift modulation based on the second data.

[0144] The secondary ripple current suppression device for angle-type medium-voltage direct-connected chain energy storage of the present invention, when used in the method of the present invention, has the same beneficial effects as the method of the present invention.

[0145] Verification section:

[0146] In a preferred embodiment of the present invention, the effectiveness of the method of the present invention is verified by building a 35kV / 10MW / 10MWh angled medium-voltage direct-connected chain energy storage system in MATLAB / Simulink simulation software.

[0147] See Figure 6 Simulated waveforms of battery current before and after applying the ripple suppression strategy of this invention to a delta-type medium-voltage direct-connected chain energy storage system operating at half-load active power. Initially, the system outputs 5MW of active power and 0MVar of reactive power. The ripple suppression strategy of this invention is applied after 2 seconds. It can be seen that before applying the suppression strategy, the peak-to-peak value of the battery ripple current is 18.12A, while after applying the suppression strategy, the peak-to-peak value of the battery ripple current becomes 4.85A. Therefore, the ripple suppression strategy of this invention attenuates the battery ripple current to 26.77% of its original value, demonstrating a significant suppression effect.

[0148] See Figure 7 Simulated waveforms of the system output current before and after incorporating the ripple suppression strategy of this invention in a delta-type medium-voltage direct-connected chain energy storage system operating under half-load active power. Figure 6 Under the same conditions, it can be seen that after adding the suppression strategy, the phase current... , and It transforms into a saddle-shaped wave, while the line current... , and Unaffected. The maximum allowed phase current specified by the system. The value is 140.7A. As can be seen from the figure, the phase current after adding the suppression strategy does not exceed the limit, and at this time k=1, the suppression effect is the best.

[0149] See Figure 8 Simulated waveforms of battery current before and after applying the ripple suppression strategy of this invention to a delta-type medium-voltage direct-connected chain energy storage system operating at full active power load. The initial full-load active power output of the system was set to 10MW, and the reactive power to 0MVar. The ripple suppression strategy of this invention was applied after 2 seconds. It can be seen that before applying the ripple suppression strategy, the peak-to-peak value of the battery ripple current was 36.07A, while after applying the ripple suppression strategy, the peak-to-peak value of the battery ripple current became 19.93A. This shows that the ripple suppression strategy of this invention reduced the battery ripple current to 55.25% of its original value. This indicates that the strategy of this invention still has a good ripple suppression effect when the system is operating at full power.

[0150] See Figure 9 Simulated waveforms of the system output current before and after incorporating the ripple suppression strategy of this invention in a delta-type medium-voltage direct-connected chain energy storage system operating at full active load. Figure 8 Under the same conditions, it can be seen that the phase current after the injection of the third harmonic does not exceed Furthermore, the line current is not affected by the third harmonic current.

[0151] See Figure 10 The simulation waveforms verifying the dynamic adjustment of the ripple current suppression strategy of this invention in a delta-type medium-voltage direct-connected chain energy storage system operating at unity power factor are shown in the figure. To verify the ability of the ripple suppression strategy of this invention to dynamically adjust the third harmonic current, the initial output active power of the system was set to 5MW, and the ripple suppression strategy of this invention was applied. The active power was stepped to 7MW and 10MW at 2s and 2.6s, respectively, and the simulation waveforms are shown in the figure. As can be seen from the figure, the ripple suppression strategy of this invention can achieve rapid adjustment of the third harmonic current when the power command changes abruptly, thereby ensuring that the phase current never exceeds the limit. Figure 10 In this context, P represents active power and Q represents reactive power.

[0152] See appendix Figure 11 Simulated waveforms of battery current before and after applying the ripple suppression strategy of this invention to a delta-type medium-voltage direct-connected chain energy storage system operating under reactive half-load conditions. The initial system output active power was set to 0 MW, and reactive power to 5 MVar. The ripple suppression strategy of this invention was applied after 2 seconds. It can be seen that before applying the suppression strategy, the peak-to-peak value of the battery ripple current was 17.31 A, while after applying the suppression strategy, the peak-to-peak value of the battery ripple current became 5.09 A. Therefore, the ripple suppression strategy of this invention reduced the battery ripple current to 29.4% of its original value. This indicates that when the system only outputs reactive power, the ripple suppression strategy of this invention has a good ripple suppression effect.

[0153] See appendix Figure 12 Simulated waveforms of the system output current before and after incorporating the ripple suppression strategy of this invention in a delta-type medium-voltage direct-connected chain energy storage system operating under reactive half-load conditions. The system operates under... Figure 11 Under the same conditions, it can be seen that after the injection of the third harmonic, the phase current does not exceed Furthermore, the line current is not affected by the third harmonic current.

[0154] See appendix Figure 13 The simulation waveforms verifying the dynamic adjustment of the ripple current suppression strategy of this invention under non-unity power factor conditions are shown in the figure. To verify the ability of the ripple suppression strategy of this invention to dynamically adjust the third harmonic current under non-unity power factor conditions, the initial output active power P of the system is set to 0 MW, and the reactive power Q is set to 10 MVar, while the ripple suppression strategy of this invention is applied. Starting from 1 second, the reactive power is reduced at a rate of 2 MVar per second, while the remaining capacity outputs active power. It can be seen that under different active and reactive power output ratios, i.e., under different... Under these conditions, the ripple suppression strategy of this invention can dynamically adjust the third harmonic current in real time, thereby ensuring that the phase current will never exceed the current limit value.

[0155] See appendix Figure 14 The simulation waveform of secondary ripple current suppression in a delta-type medium-voltage direct-connected chain energy storage system operating under phase-to-phase SOC balancing is shown. The total active power output of the three phases of the system is set to 5MW, with an additional 3MVar reactive power output from phases bc and ca, and an additional 1MVar reactive power output from phase ca, to simulate the asymmetry in phase current amplitude and phase caused by the injection of zero-sequence current during phase-to-phase SOC balancing. The ripple suppression strategy of this invention is then applied after 2 seconds. It can be seen that before the ripple suppression strategy is applied, the peak-to-peak value of the battery ripple current is 17.88A, while after applying the strategy, the peak-to-peak value becomes 6.57A. Therefore, the ripple suppression strategy of this invention reduces the ripple current to 36.74% of its original value. This demonstrates that the ripple suppression strategy of this invention has a good ripple suppression effect under three-phase current asymmetry conditions. Furthermore, as shown in the figure, the ripple suppression strategy of this invention can still ensure that the three-phase current does not exceed the required level, thus verifying the correctness and effectiveness of the ripple suppression strategy of this invention.

[0156] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for suppressing secondary ripple current in a delta-type medium-voltage direct-connected chain energy storage system, wherein the delta-type medium-voltage direct-connected chain energy storage system includes an AC filter inductor, a fuse, a contactor, and 3N H-bridge power conversion units; each H-bridge power conversion unit, i.e., a sub-module, includes a DC-side inductor, an energy storage battery, a full-bridge converter, and a DC-side capacitor, wherein the positive terminal of the full-bridge converter's DC side is connected in series with the DC-side inductor and the energy storage battery, and then connected to the negative terminal of the full-bridge converter's DC side; the DC-side capacitor is connected in parallel across the two terminals of the full-bridge converter's DC side; N H-bridge power conversion units in each phase are cascaded on the AC side to form a PCS link, and each phase PCS link is connected sequentially in a delta connection manner; each phase PCS link is connected to the AC power grid through an AC filter inductor, a fuse, and a contactor; characterized in that... include: Obtain the voltage amplitude and phase of the three-phase power grid; The three-phase active and reactive current command amplitudes are obtained based on the three-phase grid voltage amplitude and the preset active and reactive power commands; The zero-sequence current command and the additional equalization voltage of each submodule are obtained based on the state of charge of each submodule and the amplitude of the three-phase grid voltage; the three-phase current command and the third harmonic current command are obtained based on the amplitude of the three-phase active and reactive current commands, the phase of the three-phase grid voltage and the zero-sequence current command. The third harmonic current command is added to the three-phase current command and the sampled current of each phase is subtracted before being sent to the quasi-proportional resonant controller to obtain the first data of each phase; the first data of each phase is added to the additional equalization voltage to obtain the second data of each submodule; and each submodule is driven after carrier phase shift modulation is performed according to the second data. Based on the state of charge of each submodule and the amplitude of the three-phase grid voltage, the zero-sequence current command and the additional equalization voltage of each submodule are obtained, including: Obtain the state of charge (SOC) of each submodule's energy storage battery, and obtain the SOC of each phase based on the SOC. Average state of charge of three-phase energy storage batteries and the deviation of each phase-linked energy storage battery x = ab, bc, ca; According to the deviation of each phase-linked energy storage battery and the voltage amplitude of the three-phase power grid Receive zero-sequence current command pq Component amplitude and ,include: ； in, The deviation adjustment coefficient determines the speed of interphase SOC equalization. for Deviation in the ab-phase linkage energy storage battery; for Deviation in the BC phase-linked energy storage battery; According to the zero-sequence current command Component amplitude and and the three-phase grid voltage phase ab phase in Receive zero-sequence current command : ； The additional equalization voltage for each submodule includes: ； in, Indicates an additional equalizing voltage; This represents the adjustment coefficient for intraphase SOC equalization, used to adjust the equalization speed. Indicates the SOC deviation of the submodule within the phase; This represents the sampled current of each phase; and This indicates the command amplitude of the three-phase active and reactive currents; j represents the j-th submodule within a phase. N This represents the total number of submodules within a phase.

2. The method for suppressing secondary ripple current in angle-type medium-voltage direct-connected chain energy storage according to claim 1, characterized in that, The three-phase current command and the third harmonic current command are obtained based on the amplitude of the three-phase active and reactive current commands, the phase of the three-phase grid voltage, and the zero-sequence current command, including: Based on the command amplitude of the three-phase active and reactive currents and The three-phase power grid voltage phase and the zero-sequence current command Receive three-phase current command : ； The third harmonic current command is obtained based on the three-phase current command, the amplitude of the three-phase active and reactive current commands, the phase of the three-phase grid voltage, and the amplitude of the pq component of the zero-sequence current command.

3. The method for suppressing secondary ripple current in angle-type medium-voltage direct-connected chain energy storage according to claim 2, characterized in that, The third harmonic current command is obtained based on the three-phase current command, the amplitudes of the three-phase active and reactive current commands, the phase of the three-phase grid voltage, and the amplitude of the pq component of the zero-sequence current command, including: According to the three-phase current command and the three-phase grid voltage Obtain the system power factor angle ,include: The three-phase current command The Park transformation is performed, with the Park transformation rotating synchronously at an angle equal to the three-phase grid voltage. ab phase in Receive three-phase current command dq Component amplitude and : ； According to the three-phase current command Component amplitude and Obtain the system power factor angle ,include: ； According to the zero-sequence current command Component amplitude and and the three-phase active and reactive current command amplitudes and The current amplitude and phase are calculated to obtain the three-phase current amplitude. Phase with three-phase current : ； ； According to the system power factor angle The three-phase current amplitude and the phase of the three-phase current conduct Value calculation to obtain the expected value Value and Expectation The value corresponds to the phase current amplitude. ;in Value is the amplitude of the third harmonic current. With the amplitude of the fundamental frequency phase current The ratio; According to the system power factor angle The expected Value and the current amplitude The third harmonic current command is obtained. ,include: 。 4. The method for suppressing secondary ripple current in angle-type medium-voltage direct-connected chain energy storage according to claim 3, characterized in that, The process Value calculations include: When the system power factor angle When it is 0: like ,Pick phase value =1, where for The maximum allowable value of the phase current; if Solving the first equation yields phase value The first equation includes: ； in, This indicates the ratio of the phase current amplitude before and after the injection of third harmonic current in each phase; When the system power factor angle When not equal to 0: According to the angle of each phase Combined with system power factor Obtain the phase correction value of the three-phase current under asymmetrical operating conditions. and the phase correction value of the three-phase current The three-phase current phase transition value is obtained by performing interval transformation. : ； ； The fitting coefficient is obtained through the formula for calculating the fitting coefficient. , , , , Solving the second equation yields... , and Three solutions, and take phase value The second equation includes: ； In the calculation phase value Right now , and Then, take the desired value. Value And obtain the desired result. The value corresponds to the phase current amplitude. ; The fitting coefficients obtained through the fitting coefficient calculation formula include: when hour: ； when hour: 。 5. A secondary ripple current suppression device for angle-type medium-voltage direct-connected chain energy storage, used in the method described in any one of claims 1 to 4, characterized in that, The device includes a first module, a second module, and a third module; The first module is used to acquire the three-phase grid voltage amplitude and the three-phase grid voltage phase; and to obtain the three-phase active and reactive current command amplitudes based on the three-phase grid voltage amplitude and preset active and reactive power commands. The second module is used to obtain the zero-sequence current command and the additional equalization voltage of each sub-module based on the state of charge of each sub-module and the amplitude of the three-phase grid voltage; and to obtain the three-phase current command and the third harmonic current command based on the amplitude of the three-phase active and reactive current commands, the phase of the three-phase grid voltage and the zero-sequence current command. The third module is used to add the third harmonic current command to the three-phase current command and subtract the sampling current of each phase before sending it to the quasi-proportional resonant controller to obtain the first data of each phase; and to add the first data of each phase to the additional equalization voltage to obtain the second data of each sub-module. Based on the second data, carrier phase-shift modulation is performed to drive each sub-module.

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