Resonance suppression method and system for multi-machine parallel connection of network-constructed energy storage converter

Abstract

The present application relates to a method and system for suppressing resonance of multi-machine parallel grid-forming energy storage converters, which comprises multiple grid-forming energy storage converters, energy storage batteries, an energy storage monitoring platform and a controller. The grid-forming energy storage converters comprise electromagnetic interference filters. When the system is in a zero-power output state, the method injects periodic and alternating power disturbances into the multiple grid-forming energy storage converters to dynamically modulate the total output impedance of the system and destroy the fixed-frequency resonance condition. The present application can effectively suppress the resonance current without introducing any additional hardware, ensuring the safe operation of the electromagnetic interference filters and the stability of the system, and has good versatility and engineering deployability.

Description

Technical Field

[0001] This invention relates to the fields of power electronics and new energy storage technology; specifically, this invention relates to a method and system for suppressing multi-machine parallel resonance in a grid-type energy storage converter. Background Technology

[0002] With the continuous increase in the proportion of renewable energy integration, energy storage systems are playing an increasingly crucial role in stabilizing grid voltage, regulating frequency, and improving the utilization rate of renewable energy. Grid-based energy storage converters are gradually becoming an important infrastructure for future high-proportion renewable energy power systems. In practical applications, grid-based energy storage converters are often connected to a common bus in parallel with multiple devices to form a multi-machine collaborative operation system.

[0003] However, during the parallel operation of multiple units, especially when some converters are in a zero-power output state, the equivalent impedance characteristics of the AC side of the system will change. At this time, if there are harmonic components in the power grid that are close to the resonant frequency of the electromagnetic interference filter at the output end of the converter, a strong LC resonance phenomenon may be induced, resulting in abnormal amplification of AC current, which may lead to the risk of filter overheating or even burnout.

[0004] To address this issue, existing methods still have shortcomings in terms of versatility and engineering deployability. Summary of the Invention

[0005] In view of this, the present invention provides a method and system for suppressing multi-machine parallel resonance in a grid-type energy storage converter, thereby solving or at least alleviating one or more of the above-mentioned problems and other problems existing in the prior art.

[0006] To achieve the aforementioned objective, a first aspect of the present invention provides a method for suppressing multi-machine parallel resonance in a grid-connected energy storage converter, wherein the method is applied to a system connected to a power grid, the system comprising: Multiple grid-connected energy storage converters are connected in parallel, each including an electromagnetic interference filter. The energy storage battery connected to each of the aforementioned grid-type energy storage converters, The energy storage monitoring platform monitors the grid-type energy storage converter, and The controller receives monitoring data from the energy storage monitoring platform and sends control signals to the grid-type energy storage converter. The method includes the following steps: Step S1: When the system is in a zero-power output state, set the disturbance amplitude and disturbance period of the power disturbance of the grid-type energy storage converter; Step S2: Group the parallel grid-type energy storage converters into groups. One group of grid-type energy storage converters undertakes the discharge task and is responsible for outputting discharge power during the disturbance period. The other group of grid-type energy storage converters undertakes the absorption task and is responsible for absorbing charging power during the disturbance period. Step S3: During the disturbance period, each of the grid-type energy storage converters performs its assigned task according to the group, forming a power disturbance within the system. During the power disturbance, the total power absorbed is equal to the total power discharged, and the overall output power of the system to the power grid is zero. Step S4: After each disturbance cycle ends, the controller determines whether to adjust the grouping of the grid-type energy storage converter, and the grid-type energy storage converter performs a discharge task or an absorption task according to the new grouping and task. Step S5: The controller determines whether to adjust the disturbance amplitude; Step S6: When the system exits the zero-power output state, the method automatically terminates.

[0007] In the method described above, optionally, in step S2, the grouping strategy is as follows: grouping according to the serial numbers of the grid-type energy storage converters, with odd-numbered grid-type energy storage converters undertaking the discharge task, and even-numbered grid-type energy storage converters undertaking the absorption task, and... In step S4, the strategy for adjusting the grouping is as follows: the grid-type energy storage converter that undertakes the discharge task in the disturbance cycle undertakes the absorption task in the next disturbance cycle; the grid-type energy storage converter that undertakes the absorption task in the disturbance cycle undertakes the discharge task in the next disturbance cycle.

[0008] In the method described above, optionally, in step S1, the SOC of each of the energy storage batteries and the temperature of each of the electromagnetic interference filters are obtained. In step S2, based on the SOC distribution of the energy storage batteries, the parallel grid-type energy storage converters are grouped into groups to undertake discharge and absorption tasks respectively. The grid-type energy storage converters connected to the energy storage batteries with higher SOCs are assigned to perform the discharge task, while the grid-type energy storage converters connected to the energy storage batteries with lower SOCs are assigned to perform the absorption task. In step S4, the controller determines whether to adjust the grouping of the grid-type energy storage converters based on the current SOC of each of the energy storage batteries and the temperature of each of the electromagnetic interference filters. This includes: arranging the grid-type energy storage converters connected to the energy storage batteries with higher current SOCs to perform discharge tasks, and the grid-type energy storage converters connected to the energy storage batteries with lower current SOCs to perform absorption tasks. In step S5, when the temperature of the electromagnetic interference filter approaches a set threshold, the disturbance amplitude of the grid-type energy storage converter where the electromagnetic interference filter is located is automatically reduced, and the disturbance amplitude is gradually increased after the temperature of the electromagnetic interference filter recovers.

[0009] In the method described above, optionally, in step S4, a specific grid-type energy storage converter is allowed to undertake the same task for multiple consecutive disturbance cycles, and after several cycles, it is automatically determined whether to adjust the grouping of the grid-type energy storage converter.

[0010] In the method described above, optionally, in step S6, when the grid-type energy storage converter starts to perform continuous charging and discharging operation, it is determined that the system has exited the zero power output state.

[0011] In the method described above, optionally, the disturbance period satisfies: T < τ , in, T The period of the disturbance is denoted as . τ The resonant energy decay time constant, L f For filtering inductors, R d Let be the equivalent damping resistance of the system. The disturbance amplitude satisfies: Where, ΔZ inv Y is the offset of the output impedance of the grid-type energy storage converter. grid (jω res This indicates that the power grid is at the resonant frequency ω. res Admittance below.

[0012] In the method described above, optionally, the disturbance period T = 60s, and the disturbance amplitude is 1% of the rated power of the grid-type energy storage converter.

[0013] To achieve the aforementioned objective, a second aspect of the present invention provides a system using the method described in any of the first aspects above, the system comprising the grid-type energy storage converter, the energy storage battery, the energy storage monitoring platform, and the controller.

[0014] In the system described above, optionally, the grid-type energy storage converter is bidirectionally connected to the energy storage battery, the grid-type energy storage converter is bidirectionally connected to the power grid, the energy storage monitoring platform is communicatively connected to the grid-type energy storage converter and the controller, and the controller is communicatively connected to the grid-type energy storage converter.

[0015] Optionally, in the system described above, the system further includes a battery management system, a dq-axis current controller, a temperature sensor, a CAN bus, an isolation step-up transformer, and an AC bus, wherein... The battery management system monitors the status of the energy storage battery, including its state of charge (SOC), and transmits the monitoring data to the grid-connected energy storage converter. The dq-axis current controller is independently configured for each of the grid-type energy storage converters and has current loop regulation capability based on current commands. The temperature sensor is installed at the output terminal of each of the grid-type energy storage converters to monitor the thermal load level of the electromagnetic interference filter. The CAN bus is communicatively connected to the grid-type energy storage converter, the energy storage monitoring platform, and the controller. The grid-type energy storage converter communicates with the energy storage monitoring platform via the CAN bus, and the controller communicates with the grid-type energy storage converter via the CAN bus. The isolation step-up transformer isolates the grid-type energy storage converter from the direct electrical connection with the power grid and raises the voltage output by the grid-type energy storage converter to a voltage level suitable for the power grid. The AC bus transmits electrical energy to or obtains electrical energy from the power grid, and the grid-type energy storage converter is connected to the AC bus through the isolation step-up transformer.

[0016] The multi-machine parallel resonance suppression method and system of the grid-type energy storage converter of the present invention can effectively suppress the resonant current without introducing any additional hardware, ensure the safe operation of the electromagnetic interference filter and the stability of the system, and has good versatility and engineering deployability. Attached Figure Description

[0017] The disclosure of this invention will become more apparent from the accompanying drawings. It should be understood that these drawings are for illustrative purposes only and are not intended to limit the scope of protection of this invention. In the drawings: Figure 1This is a schematic block diagram of an embodiment of the multi-machine parallel resonance suppression system for grid-type energy storage converters of the present invention; Figure 2 This is a flowchart illustrating an embodiment of the multi-machine parallel resonance suppression method for grid-type energy storage converters of the present invention. Detailed Implementation

[0018] Referring to the accompanying drawings and specific embodiments, the structure, composition, characteristics, and advantages of the multi-machine parallel resonance suppression method and system for grid-type energy storage converters of the present invention will be described below by way of example. However, all descriptions should not be used to limit the present invention in any way.

[0019] Furthermore, for any single technical feature described or implied in the embodiments mentioned herein, or any single technical feature shown or implied in the various figures, the present invention still allows for any combination or deletion of these technical features (or their equivalents) without any technical obstacle, and thus these further embodiments according to the present invention should also be considered within the scope of this description.

[0020] Figure 1 This is a schematic block diagram of an embodiment of the multi-machine parallel resonance suppression system for grid-type energy storage converters of the present invention.

[0021] As shown in the figure, in this embodiment, the system is connected to the power grid, and the equivalent impedance of the power grid is Z. grid (s), the system includes n grid-type energy storage converters (PCS1-PCSn in the figure), energy storage batteries (batteries in the figure), battery management system (BMS in the figure), isolation step-up transformer (isolation step-up transformer in the figure), AC bus, CAN bus, energy storage monitoring platform and controller.

[0022] As shown in the figure, in this embodiment, the grid-type energy storage converters are connected in parallel and connected to the energy storage batteries, and are also connected to the AC bus through isolation step-up transformers to control the bidirectional flow of electrical energy between the energy storage batteries and the AC bus. The battery management system collects the SOC (State of Charge) information of the energy storage batteries and transmits it to the grid-type energy storage converters. The grid-type energy storage converters communicate with the energy storage monitoring platform and controller through the CAN bus to transmit information such as disturbance groups, disturbance signals, and temperature. The controller receives information from the energy storage monitoring platform and the power grid, and sends control signals to the grid-type energy storage converters to ensure the synchronous execution of power commands and disturbance cycles. The entire system can be uniformly scheduled by the controller. The AC bus is connected to the power grid through isolation step-up transformers to transmit electrical energy to the power grid or obtain electrical energy from the power grid.

[0023] In this embodiment, the system also includes an electromagnetic interference (EMI) filter, a temperature sensor, and a dq-axis current controller (not directly shown in the figure). The EMI filter and temperature sensor are located at the output of each grid-connected energy storage converter. The temperature sensor monitors the thermal load level of the EMI filter in real time to sense its operating status. Furthermore, each grid-connected energy storage converter is equipped with an independent dq-axis current controller. The dq axis refers to the two DC components obtained by projecting the AC quantities in the three-phase stationary coordinate system onto the dq coordinate system, which rotates synchronously with the grid voltage vector, through the Park transformation. The d-axis is in the same direction as the grid voltage vector, and the q-axis is perpendicular to the d-axis. The d-axis current controls active power, and the q-axis current controls reactive power. This dq-axis current controller supports high-bandwidth current loop regulation capabilities, ensuring rapid switching at micro-power levels within a short time.

[0024] In this embodiment, the controller performs multi-machine collaborative group control to generate periodic alternating disturbances, thereby achieving impedance frequency characteristic modulation and thus realizing resonance suppression.

[0025] Specifically, multi-machine cooperative group control includes dividing multiple grid-type energy storage converters operating in parallel into odd-numbered groups and even-numbered groups. The odd-numbered groups output a small amount of discharge power per unit time, while the even-numbered groups absorb a proportional amount of charging power. In some preferred embodiments, the grouping can be optimized based on the SOC of the corresponding energy storage battery for each grid-type energy storage converter. Under the premise of meeting the disturbance design requirements for the total charging and discharging disturbance power, grid-type energy storage converters with higher connected energy storage battery SOCs are preferentially selected to undertake the discharge task, while grid-type energy storage converters with lower connected energy storage battery SOCs undertake the absorption task, thereby achieving a dual-objective control strategy of resonance suppression and SOC self-balancing.

[0026] Specifically, the periodic alternating disturbance includes: within a fixed disturbance period T, odd-numbered and even-numbered grid-type energy storage converters alternately switch their charging and discharging roles, thereby constructing a continuous dynamic disturbance mechanism. This disturbance process operates in conjunction with a SOC priority strategy to ensure that while maintaining the overall disturbance power balance, a dynamic balance of the system charge distribution is continuously achieved.

[0027] Specifically, impedance frequency characteristic modulation includes: under the above-mentioned disturbance mechanism, the grid-type energy storage converter exhibits different output impedance characteristics under different charging and discharging states, causing the equivalent impedance of the system to change periodically with time, effectively interfering with the resonant coupling relationship between the grid harmonic frequency points, thereby breaking the fixed resonance condition.

[0028] Specifically, resonance suppression is achieved by setting the disturbance period T to be less than the resonance energy accumulation time constant τ, which allows the disturbance state to be switched before the resonance energy has accumulated effectively, thereby disrupting the continuous excitation process of the resonance energy, suppressing the harmonic current amplification phenomenon, and improving the safety and robustness of the system operation.

[0029] Furthermore, this embodiment reveals the mechanism of its resonance suppression, including the equivalent impedance reconstruction mechanism and frequency domain stability analysis.

[0030] Specifically, the equivalent impedance reconstruction mechanism includes: due to the difference in output impedance characteristics of the grid-type energy storage converter under charging and discharging states, periodic micro-power disturbances will cause dynamic changes in the equivalent admittance matrix of the system, thereby disrupting the original resonance matching conditions.

[0031] Specifically, the frequency domain stability analysis includes: assuming the output impedance of a single grid-connected energy storage converter is Z. inv (s), the equivalent impedance of the power grid is Z grid If (s), then the frequency domain stability of the system can be expressed by the generalized Nyquist criterion as follows: Among them, Y grid (s) represents the admittance form of the grid impedance. Through periodic perturbation Z... inv The real part (equivalent resistance) and imaginary part (equivalent reactance) of (s) are used to prevent the eigenvalue locus of the closed-loop transfer function from crossing the unstable region, thereby maintaining the system's resonant stability.

[0032] Furthermore, this embodiment provides a design basis for key parameters: the power disturbance amplitude should meet the following requirements. To ensure that the disturbance amplitude of the output impedance of the grid-connected energy storage converter is sufficient to escape the resonant matching frequency band with the grid impedance; the disturbance period T should satisfy: T < τ ,in, τ The resonant energy decay time constant L f For the filter inductor, R d It serves as the system's equivalent damping resistance, interrupting the accumulation of resonant energy and achieving a dynamic suppression effect.

[0033] Furthermore, to enhance the thermal safety performance of the system, this embodiment also introduces an adaptive disturbance power adjustment mechanism based on the temperature rise state of the electromagnetic interference filter. Specifically, the controller monitors the temperature change of the electromagnetic interference filter in real time. When the temperature rise trend is detected to be close to a preset threshold, the micro-power disturbance amplitude is automatically reduced to decrease heat accumulation in the electromagnetic interference filter and prevent thermal damage caused by excessive disturbance. This thermal protection mechanism further improves the applicability, long-term stability, and robustness of the system and its resonance suppression method in this embodiment without interfering with the resonance suppression effect.

[0034] Figure 2 This is a flowchart illustrating an embodiment of the multi-machine parallel resonance suppression method for grid-type energy storage converters of the present invention.

[0035] As shown in the figure, in this embodiment, the method includes the following steps: Step S1: When the system is in a zero-power output state, set the initial disturbance period T and the converter disturbance power amplitude P according to the system design. pert At the same time, the initial SOC value of the energy storage cluster connected to each converter is obtained; Step S2: Based on the SOC distribution, the parallel converters are grouped into groups to undertake the tasks of discharging and absorbing disturbances, forming power disturbance pairs within the system. The converters with higher SOC are prioritized to perform discharge disturbances in order to achieve dynamic energy self-balancing. Step S3: Each converter performs micro-power level charging and discharging disturbance operations according to its group role and on a periodic basis. During the disturbance process, the total active power between the system and the grid is kept to zero, and dynamic power exchange is only formed within the system, thereby introducing periodic modulation of the output impedance. Step S4: After each disturbance cycle, the controller updates the SOC and filter temperature rise status of each unit, and decides whether to adjust the grouping structure or power amplitude based on the evaluation results to deal with problems such as SOC offset or uneven heat load. Step S5: When the filter temperature of a converter is detected to be close to the set threshold, the controller automatically reduces its disturbance amplitude to reduce current surges and alleviate thermal stress. After the temperature recovers, the disturbance power is gradually increased again, achieving coordinated control of disturbance and thermal management; and Step S6: When the system detects that the converter has started to perform continuous high-power charging / discharging operation, it indicates that it has exited the zero-power state. The parallel resonance suppression mechanism is automatically terminated, and the controller switches to the conventional power control logic to ensure a smooth transition of the system.

[0036] Among them, the zero power output state refers to the system as a whole exchanging zero average active power with the grid. The converter mentioned above is a grid-type energy storage converter, the energy storage cluster mentioned above is an energy storage unit that integrates energy storage batteries and a battery management system, and the filter mentioned above is an electromagnetic interference filter.

[0037] When multiple grid-connected energy storage converters in the system operate in parallel and are in a zero-power output state, this method can effectively suppress the LC resonance phenomenon caused by the interaction between the electromagnetic interference filter and grid harmonics. This method achieves dynamic modulation of the system's total output impedance by injecting small-amplitude, periodically alternating micro-power disturbances into multiple grid-connected energy storage converters, thereby disrupting the fixed-frequency resonance condition and preventing frequency matching between the system's impedance frequency response and the grid background harmonics.

[0038] In zero-power output mode, some grid-connected energy storage converters are allowed to perform brief discharge operations with minimal power per unit time, while other grid-connected energy storage converters simultaneously absorb an equal amount of power to form a micro-charging process, achieving dynamic balance of power disturbances within the system. Correspondingly, the DC side of the energy storage units connected to each grid-connected energy storage converter will participate in micro-amplitude charging and discharging behavior, and their SOC will also fluctuate slowly. Therefore, this embodiment introduces a SOC-oriented grouping strategy, which, while meeting the disturbance control objective, further achieves adaptive balance of energy distribution among energy storage batteries.

[0039] In step S1 above, specifically, during the control strategy initialization phase, the set disturbance period T should satisfy: T < τ, where τ is the resonant energy decay time constant. L f For the filter inductor, R d This is the equivalent damping resistance of the system. Under the premise that the disturbance period T is less than the energy accumulation time constant τ of the system's inductor-capacitor resonant circuit, the resonant energy is interrupted by the active disturbance before it is fully established, thus achieving root-cause suppression of the LC resonance phenomenon. In this embodiment, T = 60s, and the amplitude of a single disturbance is set to 1% of the rated power P. N That is, P pert = 0.01P N .

[0040] In step S2 above, specifically, in this embodiment there are three grid-type energy storage converters, numbered PCS1, PCS2 and PCS3. Based on the SOC information of each energy storage battery at the initial moment, the grid-type energy storage converters PCS1 and PCS3 connected to the energy storage battery with higher SOC are divided into odd groups, and the grid-type energy storage converter PCS2 connected to the energy storage battery with lower SOC is divided into even groups, thus establishing the first round of disturbance groups.

[0041] In an optional embodiment, step S2 above can be modified to: dividing the multiple grid-type converters operating in parallel into an odd-numbered group and an even-numbered group, wherein the odd-numbered group of converters outputs a small amount of discharge power per unit time, and the even-numbered group of converters absorbs a proportional amount of charging power.

[0042] In step S3 above, specifically, during the first disturbance period, in this embodiment, the odd-array grid-type energy storage converters PCS1 and PCS3 each output 0.01P. N Power is supplied to the AC bus, and the even-array grid-type energy storage converter PCS2 absorbs an equivalent total power of 0.02P. N This creates internal power disturbances within the system; while maintaining the system's overall output power to the power grid at zero, it effectively disturbs the system's output impedance characteristics.

[0043] In step S4 above, specifically, in subsequent disturbance cycles, whether the system performs odd-even group switching is no longer fixed according to a rotation rhythm. Instead, the controller dynamically determines whether to switch charging / discharging roles or adjust the grouping structure after each disturbance cycle based on the latest SOC distribution and the thermal state of the electromagnetic interference filter. Regarding SOC regulation, to avoid SOC imbalance in energy storage batteries due to long-term disturbances, the controller re-evaluates the grouping structure based on the latest SOC information after each disturbance cycle. It prioritizes grid-type energy storage converters connected to energy storage batteries with higher SOCs to undertake discharge tasks, while grid-type energy storage converters connected to energy storage batteries with lower SOCs undertake absorption tasks, achieving dynamic energy balance among the energy storage batteries. If the SOC difference is large within a certain cycle, the controller can also maintain the current grouping, allowing specific grid-type energy storage converters to participate in discharge or charging for multiple consecutive disturbance cycles to accelerate SOC convergence. However, to prevent uneven load on the electromagnetic interference filter and imbalance of the disturbance strategy, the controller is equipped with a disturbance cycle evaluation mechanism. After a disturbance cycle, it will automatically determine whether the groups need to be reclassified to ensure that the system achieves optimal coordination among resonance suppression, thermal management and SOC balance.

[0044] In step S5 above, specifically considering the potential heat accumulation in the electromagnetic interference filters due to disturbance operations, the system also introduces a disturbance amplitude adaptive mechanism based on temperature rise. The controller monitors the temperature of each electromagnetic interference filter in real time. When the detected temperature approaches a set threshold, it automatically reduces the disturbance power amplitude of that grid-type energy storage converter, such as by 2%P. N Reduced to 0.5% P N This reduces the peak current, alleviates the thermal load on the electromagnetic interference filter, and gradually restores the disturbance intensity after the temperature drops, thus achieving closed-loop regulation of disturbance control and thermal management.

[0045] In step S6 above, specifically, when it is detected that any grid-type energy storage converter exits the zero-power output mode, that is, starts to perform continuous charging and discharging tasks, the disturbance logic will automatically terminate and restore the normal power control process.

[0046] Parallel resonance refers to the risk of high-frequency resonant coupling between the electromagnetic interference filter and the grid background impedance in scenarios where multiple grid-connected energy storage converters operate in parallel. This risk is particularly pronounced under zero-power output conditions, where the system impedance frequency response is more likely to match the grid harmonic frequencies, leading to LC resonance. Traditional resonance suppression methods mostly focus on the active power operation phase and lack effective control measures for boundary operating states.

[0047] As shown in steps S1-S6 above, the disturbance strategy proposed in this embodiment can inject periodically alternating internal micro-power disturbances when the system is in a zero-power output state, dynamically adjust the equivalent output impedance of each grid-type energy storage converter, break the static characteristics of its frequency domain response, and then reconstruct and optimize the overall frequency response behavior of the system, effectively reduce the coupling strength between the system and the grid harmonic impedance, and provide a strategic solution for parallel resonance suppression without additional hardware.

[0048] Specifically, in a parallel grid-connected energy storage converter system, the output impedance of any grid-connected energy storage converter can be expressed as a complex domain function: Where R(s) and X(s) are the real and imaginary parts of the output equivalent impedance of the grid-type energy storage converter, and s=jω is the Laplace variable.

[0049] When multiple grid-type energy storage converters are connected in parallel, their total output impedance Z eq (s) can be calculated by superimposing the impedances of each grid-type energy storage converter in parallel. If all grid-type energy storage converters are in a static zero-power state, the overall output impedance of the system remains stable, and it is very easy for it to resonate with the grid-side impedance Z at certain frequency points. grid The resonant points of (s) coincide, leading to an enhanced power frequency response and inducing LC resonance.

[0050] Some embodiments of the present invention force a momentary change in the output impedance of some grid-connected energy storage converters by periodically injecting small disturbance power. According to the classical impedance model, the output impedance can be approximately expressed as: Among them, L f For the filter inductor, K p K i These are the parameters for the dq-axis current controller. When the current command changes, the operating point of the dq-axis current controller shifts, resulting in an actual output impedance Z. inv This generates considerable disturbance.

[0051] The effect of this disturbance in the frequency domain can be expressed as follows: During the disturbance period, the equivalent impedance magnitude Z of the system increases. eqIt is no longer a constant value, but fluctuates with a disturbance period T, and the frequency fluctuates accordingly, satisfying: Among them, Z base (jω) is the reference impedance frequency response of the system under steady-state zero power output, and ΔZ(jω,kT) is the impedance offset caused by the disturbance in the kth disturbance period.

[0052] The disturbance operation causes the system's equivalent output impedance to fluctuate periodically over time, breaking its fixed response characteristics in the frequency domain and thus weakening the resonant coupling with the harmonic frequencies of the power grid.

[0053] The entire method of this embodiment can be implemented without introducing any additional hardware, only by optimizing the control logic. It has good versatility and engineering deployability, and is suitable for various grid-type energy storage scenarios such as microgrid island standby and grid-connected backup.

[0054] Some embodiments of the present invention do not require additional hardware devices and achieve resonance suppression only through control strategy optimization. They have the advantages of high efficiency, easy deployment, and strong robustness, and are suitable for ensuring the safe operation of electromagnetic interference filters in large-scale grid-type energy storage systems.

[0055] Some embodiments of the present invention have one or more of the following beneficial effects: (1) No new hardware devices are required. Effective suppression of AC side resonance can be achieved simply by optimizing the existing variable control strategy. It does not rely on additional sensors, resistive dampers or complex high-frequency impedance shaping algorithms, which significantly reduces the system deployment cost and has good engineering feasibility and application value.

[0056] (2) By injecting periodically alternating micro-power disturbances between multiple grid-type energy storage converters, the system output impedance changes dynamically with time, thereby actively disrupting the matching relationship between the grid harmonic frequency and the filter resonant frequency, essentially destroying the stable matching condition of the resonant frequency, and thus achieving source suppression of resonant energy accumulation from the frequency response level.

[0057] (3) An adaptive disturbance power adjustment mechanism based on temperature rise was designed. To address the potential thermal load problem of the electromagnetic interference filter during long-term operation, the disturbance amplitude can be dynamically adjusted according to the real-time temperature change of the electromagnetic interference filter, effectively suppressing the risk of heat accumulation and significantly improving the system's operational stability and thermal safety margin.

[0058] (4) Innovatively, the SOC of the energy storage battery is used as the basis for disturbance grouping. While meeting the requirements for resonance suppression, the grid-type energy storage converter connected to the energy storage battery with a high SOC participates in the discharge disturbance, while the grid-type energy storage converter connected to the energy storage battery with a low SOC undertakes the absorption task. This achieves adaptive balance of power among energy storage units and further improves the consistency of system operation and the performance throughout the entire life cycle.

[0059] (5) Applicable to boundary operation scenarios such as zero power output state, especially suitable for grid-type energy storage systems in zero power output state operation scenarios, such as island standby, standby parallel, etc. Compared with most existing resonance suppression methods that focus on the active operation stage, it fills the gap in resonance suppression technology under zero power mode, and significantly improves the operational safety and robustness of microgrids and distributed energy storage systems under boundary conditions.

[0060] The technical scope of this invention is not limited to the contents of the above specification. Those skilled in the art can make various modifications and variations to the above embodiments without departing from the technical concept of this invention, and all such modifications and variations should fall within the scope of this invention.

Claims

1. A method for suppressing multi-machine parallel resonance in a grid-type energy storage converter, characterized in that, The method is applied to a system connected to a power grid, the system comprising: Multiple grid-connected energy storage converters are connected in parallel, each including an electromagnetic interference filter. The energy storage battery connected to each of the aforementioned grid-type energy storage converters, The energy storage monitoring platform monitors the grid-type energy storage converter, and The controller receives monitoring data from the energy storage monitoring platform and sends control signals to the grid-type energy storage converter. The method includes the following steps: Step S1: When the system is in a zero-power output state, set the disturbance amplitude and disturbance period of the power disturbance of the grid-type energy storage converter; Step S2: Group the parallel grid-type energy storage converters into groups. One group of grid-type energy storage converters undertakes the discharge task and is responsible for outputting discharge power during the disturbance period. The other group of grid-type energy storage converters undertakes the absorption task and is responsible for absorbing charging power during the disturbance period. Step S3: During the disturbance period, each of the grid-type energy storage converters performs its assigned task according to the group, forming a power disturbance within the system. During the power disturbance, the total power absorbed is equal to the total power discharged, and the overall output power of the system to the power grid is zero. Step S4: After each disturbance cycle ends, the controller determines whether to adjust the grouping of the grid-type energy storage converter, and the grid-type energy storage converter performs a discharge task or an absorption task according to the new grouping and task. Step S5: The controller determines whether to adjust the disturbance amplitude; Step S6: When the system exits the zero-power output state, the method automatically terminates.

2. The method as described in claim 1, characterized in that, In step S2, the grouping strategy is as follows: the grid-type energy storage converters are grouped according to their serial numbers; those with odd-numbered serial numbers undertake the discharge task, and those with even-numbered serial numbers undertake the absorption task. In step S4, the strategy for adjusting the grouping is as follows: the grid-type energy storage converter that undertakes the discharge task in the disturbance cycle undertakes the absorption task in the next disturbance cycle; the grid-type energy storage converter that undertakes the absorption task in the disturbance cycle undertakes the discharge task in the next disturbance cycle.

3. The method as described in claim 1, characterized in that, In step S1, the SOC of each of the energy storage batteries and the temperature of each of the electromagnetic interference filters are obtained. In step S2, based on the SOC distribution of the energy storage batteries, the parallel grid-type energy storage converters are grouped into groups to undertake discharge and absorption tasks respectively. The grid-type energy storage converters connected to the energy storage batteries with higher SOCs are assigned to perform the discharge task, while the grid-type energy storage converters connected to the energy storage batteries with lower SOCs are assigned to perform the absorption task. In step S4, the controller determines whether to adjust the grouping of the grid-type energy storage converters based on the current SOC of each of the energy storage batteries and the temperature of each of the electromagnetic interference filters. This includes: arranging the grid-type energy storage converters connected to the energy storage batteries with higher current SOCs to perform discharge tasks, and the grid-type energy storage converters connected to the energy storage batteries with lower current SOCs to perform absorption tasks. In step S5, when the temperature of the electromagnetic interference filter approaches a set threshold, the disturbance amplitude of the grid-type energy storage converter where the electromagnetic interference filter is located is automatically reduced, and the disturbance amplitude is gradually increased after the temperature of the electromagnetic interference filter recovers.

4. The method as described in claim 3, characterized in that, In step S4, a specific grid-type energy storage converter is allowed to undertake the same task for multiple consecutive disturbance cycles, and after several cycles, it is automatically determined whether to adjust the grouping of the grid-type energy storage converter.

5. The method as described in claim 1, characterized in that, In step S6, when the grid-type energy storage converter starts to perform continuous charging and discharging operation, it is determined that the system has exited the zero power output state.

6. The method as described in claim 1, characterized in that, The disturbance period satisfies: T < τ ， in, T The period of the disturbance is denoted as . τ The resonant energy decay time constant, L f For filtering inductors, R d Let be the equivalent damping resistance of the system. The disturbance amplitude satisfies: Where, ΔZ inv Y is the offset of the output impedance of the grid-type energy storage converter. grid (jω res This indicates that the power grid is at the resonant frequency ω. res Admittance below.

7. The method as described in claim 6, characterized in that, The disturbance period is T=60s, and the disturbance amplitude is 1% of the rated power of the grid-type energy storage converter.

8. A system using the method of any one of claims 1-7, the system comprising the grid-type energy storage converter, the energy storage battery, the energy storage monitoring platform, and the controller.

9. The system as described in claim 8, characterized in that, The grid-type energy storage converter is bidirectionally connected to the energy storage battery, the grid-type energy storage converter is bidirectionally connected to the power grid, the energy storage monitoring platform is communicatively connected to the grid-type energy storage converter and the controller, and the controller is communicatively connected to the grid-type energy storage converter.

10. The system as described in claim 8, characterized in that, The system also includes a battery management system, a dq-axis current controller, a temperature sensor, a CAN bus, an isolation step-up transformer, and an AC bus. The battery management system monitors the status of the energy storage battery, including its state of charge (SOC), and transmits the monitoring data to the grid-connected energy storage converter. The dq-axis current controller is independently configured for each of the grid-type energy storage converters and has current loop regulation capability based on current commands to control the power of the grid-type energy storage converters. The temperature sensor is installed at the output terminal of each of the grid-type energy storage converters to monitor the thermal load level of the electromagnetic interference filter. The CAN bus is communicatively connected to the grid-type energy storage converter, the energy storage monitoring platform, and the controller. The grid-type energy storage converter communicates with the energy storage monitoring platform via the CAN bus, and the controller communicates with the grid-type energy storage converter via the CAN bus. The isolation step-up transformer isolates the grid-type energy storage converter from the direct electrical connection with the power grid and raises the voltage output by the grid-type energy storage converter to a voltage level suitable for the power grid. The AC bus transmits electrical energy to or obtains electrical energy from the power grid, and the grid-type energy storage converter is connected to the AC bus through the isolation step-up transformer.

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