Harmonic conducted interference suppression method based on flywheel energy storage

Abstract

The invention relates to the technical field of flywheel energy storage, and discloses a harmonic conducted interference suppression method based on flywheel energy storage. The method comprises the following steps: collecting current and voltage signals of a direct current bus side of the flywheel energy storage system in real time, separating fundamental and harmonic components through frequency domain decomposition, and then calculating current and voltage harmonic characteristic parameters; and after comparison with a preset harmonic threshold value, a harmonic suppression reference point is dynamically set, and a progressive suppression signal of which the suppression intensity change rate is adjusted by a slope control module is injected into the reference point. Generating a rotating speed compensation coefficient by combining the coupling relationship between the harmonic characteristic parameter and the flywheel rotor rotating speed, and adjusting the suppression signal slope in real time; the adjusted signal is diffused to the overall system through a chain type conduction mechanism, meanwhile, the harmonic suppression feedback quantity is monitored to update the threshold condition, datum point setting and signal adjustment are repeated until the harmonic characteristic parameters meet the convergence criterion, and stable operation of the system can be guaranteed.

Description

Technical Field

[0001] This invention relates to the field of flywheel energy storage technology, specifically to a method for suppressing harmonic conduction interference based on flywheel energy storage. Background Technology

[0002] Currently, the main technical means for harmonic suppression in flywheel energy storage systems include passive filtering and active filtering. Passive filtering technology uses a filter network composed of capacitors, inductors, and resistors connected in series or parallel on the DC bus side to suppress harmonics by utilizing the impedance characteristics of the filter elements for specific frequency harmonics. However, passive filtering schemes have drawbacks such as fixed filtering frequency bands, poor adaptability to harmonics with varying frequencies, large size and weight, and susceptibility to resonance with the system, making it difficult to meet the requirements of high-power flywheel energy storage systems for wide-band, dynamic harmonic suppression. Active filtering technology, on the other hand, detects harmonic components in the system and actively injects a compensation current or voltage equal in magnitude but opposite in phase with the harmonic components using the power converter, thereby achieving dynamic cancellation of harmonics. However, existing active filtering methods still have many shortcomings when applied to flywheel energy storage systems: most active filtering schemes use fixed harmonic suppression reference points and suppression signal strengths, and cannot be dynamically adjusted according to the real-time changes of harmonic components on the DC bus side. When the harmonic frequency and amplitude fluctuate, the suppression effect will decrease significantly. Existing technologies often ignore the coupling relationship between flywheel rotor speed and harmonic components. During the acceleration, deceleration or stable operation of the flywheel rotor, its speed change will affect the harmonic characteristics on the DC bus side through electromagnetic coupling. If the suppression signal is not adjusted in a timely manner, it is easy to cause harmonic suppression to lag or overcompensate, further aggravating the harmonic interference problem of the system.

[0003] Most existing harmonic suppression methods employ a single-point suppression mode, injecting suppression signals only at specific locations on the DC bus. This makes it difficult to rapidly spread the suppression effect throughout the entire flywheel energy storage system, resulting in uneven harmonic suppression effects across different areas of the system, and leaving some critical nodes at risk of exceeding harmonic limits. Furthermore, most solutions lack a robust feedback adjustment mechanism, failing to update control parameters in real time based on the actual effect of harmonic suppression. This hinders closed-loop optimization of the harmonic suppression process and makes the system susceptible to system parameter drift and external interference during long-term operation, leading to a gradual degradation of suppression performance. These problems make existing harmonic suppression technologies ineffective in addressing harmonic conduction interference issues in flywheel energy storage systems under complex operating conditions, necessitating a new technological solution capable of dynamic, adaptive, and global harmonic suppression. Summary of the Invention

[0004] The purpose of this invention is to provide a method for suppressing harmonic conduction interference based on flywheel energy storage, so as to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides a method for suppressing harmonic conducted interference based on flywheel energy storage, the method comprising: Real-time acquisition of current and voltage signals on the DC bus side of the flywheel energy storage system; The current and voltage signals are decomposed in the frequency domain to separate the fundamental and harmonic components. Harmonic characteristic parameters are calculated and generated based on the harmonic components, including current harmonic characteristic parameters and voltage harmonic characteristic parameters. The harmonic suppression benchmark point is dynamically set by comparing the preset harmonic threshold conditions with the harmonic characteristic parameters. A progressive harmonic suppression signal is injected at the harmonic suppression reference point, and the rate of change of the suppression intensity of the progressive harmonic suppression signal is adjusted by a slope control module. Based on the coupling relationship between the harmonic characteristic parameters and the flywheel rotor speed, a speed compensation coefficient is generated; The slope of the progressive harmonic suppression signal is adjusted in real time using the speed compensation coefficient. The adjusted progressive harmonic suppression signal is diffused from a single point injection to the entire flywheel energy storage system through a chain-like suppression conduction mechanism. The harmonic suppression feedback of the current signal and voltage signal is monitored in real time, and the harmonic threshold condition is updated according to the harmonic suppression feedback. Repeat the dynamic setting of the harmonic suppression reference point and the adjustment of the progressive harmonic suppression signal until the harmonic characteristic parameters meet the preset convergence criteria.

[0006] Preferably, the frequency domain decomposition of the current signal and voltage signal includes: The current signal is decomposed into fundamental current components and harmonic current components using a fast Fourier transform. The voltage signal is simultaneously decomposed into fundamental voltage components and harmonic voltage components using a fast Fourier transform. The amplitude and phase information of the current harmonic components are extracted to generate current harmonic characteristic parameters; The amplitude and phase information of the voltage harmonic components are extracted to generate voltage harmonic characteristic parameters.

[0007] Preferably, the dynamic setting of the harmonic suppression reference point includes: When the current harmonic characteristic parameter exceeds the first harmonic threshold, the current flywheel power conversion unit node is set as the first harmonic suppression reference point; When the voltage harmonic characteristic parameter exceeds the second harmonic threshold, the current flywheel bus connection node is set as the second harmonic suppression reference point; When the current harmonic characteristic parameter and the voltage harmonic characteristic parameter both exceed the third harmonic threshold, the central control node of the flywheel energy storage system is set as the main harmonic suppression reference point.

[0008] Preferably, injecting a progressive harmonic suppression signal at the harmonic suppression reference point includes: A first type of progressive harmonic suppression signal is injected at the first harmonic suppression reference point; A second type of progressive harmonic suppression signal is injected at the second harmonic suppression reference point; A global progressive harmonic suppression signal is injected at the main harmonic suppression reference point; The first type of progressive harmonic suppression signal, the second type of progressive harmonic suppression signal, and the global progressive harmonic suppression signal all adjust the initial suppression intensity change rate through an independent slope control module.

[0009] Preferably, the generated speed compensation coefficient includes: Real-time acquisition of the current rotational speed of the flywheel rotor; The first speed coupling factor is generated by multiplying the current harmonic characteristic parameters with the current speed of the flywheel rotor. The second speed coupling factor is generated by multiplying the voltage harmonic characteristic parameters with the current speed of the flywheel rotor. The arithmetic mean of the first speed coupling factor and the second speed coupling factor is used as the speed compensation coefficient.

[0010] Preferably, the real-time adjustment of the slope of the progressive harmonic suppression signal using the rotational speed compensation coefficient includes: The speed compensation coefficient is input into the slope control module of the first type of progressive harmonic suppression signal, and the initial suppression intensity change rate is scaled proportionally. The speed compensation coefficient is input into the slope control module of the second type of progressive harmonic suppression signal to scale the rate of change of the initial suppression intensity proportionally. The speed compensation coefficient is input into the slope control module of the global progressive harmonic suppression signal, and the initial suppression intensity change rate is scaled proportionally.

[0011] Preferably, the chain-like inhibition conduction mechanism includes: The harmonic suppression state quantity of the first harmonic suppression reference point is transferred to the adjacent flywheel power conversion unit node; The harmonic suppression state quantity of the second harmonic suppression reference point is transferred to the adjacent flywheel bus connection node; Broadcast the harmonic suppression state of the main harmonic suppression reference point to all flywheel energy storage subsystem nodes; The progressive harmonic suppression signal parameters are updated synchronously between adjacent nodes based on the harmonic suppression state quantity.

[0012] Preferably, updating the harmonic threshold condition based on the harmonic suppression feedback includes: The rate of decrease of the current harmonic characteristic parameters is calculated in real time to generate current harmonic suppression feedback. The rate of decrease of the voltage harmonic characteristic parameters is calculated in real time to generate voltage harmonic suppression feedback. When the current harmonic suppression feedback quantity is continuously lower than the preset update threshold, the trigger thresholds of the first harmonic threshold and the third harmonic threshold are increased. When the voltage harmonic suppression feedback quantity is continuously lower than the preset update threshold, the trigger thresholds of the second harmonic threshold and the third harmonic threshold are increased.

[0013] Preferably, repeatedly performing the dynamic setting of the harmonic suppression reference point includes: Based on the updated first harmonic threshold, re-determine whether the power conversion unit node should be set as the first harmonic suppression reference point; Based on the updated second harmonic threshold, re-determine whether the bus connection node should be set as the second harmonic suppression reference point; The central control node should be re-determined as the primary harmonic suppression reference point based on the updated third harmonic threshold.

[0014] Preferably, the convergence criterion until the harmonic characteristic parameters satisfy the preset convergence criteria includes: The current harmonic characteristic parameter is lower than the first convergence threshold for three consecutive sampling values. The voltage harmonic characteristic parameter is lower than the second convergence threshold for three consecutive sampling values. The ratio of the current harmonic characteristic parameter to the voltage harmonic characteristic parameter is stably maintained within a preset range.

[0015] Compared with the prior art, the beneficial effects of the present invention are: By acquiring current and voltage signals from the DC bus side of the flywheel energy storage system in real time, frequency domain decomposition is performed on the acquired signals to separate the fundamental and harmonic components, clearly defining the specific composition of harmonic interference. Current and voltage harmonic characteristic parameters are calculated based on the harmonic components, allowing for quantifiable characterization of harmonics and facilitating precise comparison with preset harmonic threshold conditions, thereby dynamically setting the harmonic suppression benchmark. A progressive harmonic suppression signal is injected at the benchmark, and the rate of change of suppression intensity is adjusted via a slope control module to achieve a smooth transition of the suppression signal. Simultaneously, a speed compensation coefficient is generated based on the coupling relationship between the harmonic characteristic parameters and the flywheel rotor speed. This coefficient is used to adjust the slope of the progressive harmonic suppression signal in real time, fully considering the impact of flywheel rotor speed changes on harmonic characteristics, enabling the suppression signal to adaptively adjust to speed variations. By using a chain-like suppression and conduction mechanism, the adjusted progressive harmonic suppression signal is diffused from a single point injection to the entire flywheel energy storage system. This changes the uneven suppression effect of the traditional single-point suppression mode, ensuring that all key nodes in the system (such as the output end of the power electronic conversion device, the flywheel rotor drive end, and the sensor signal acquisition end) can be effectively suppressed by harmonics.

[0016] By real-time monitoring of harmonic suppression feedback in current and voltage signals and updating harmonic threshold conditions based on the feedback, a comprehensive closed-loop regulation mechanism is constructed, enabling continuous optimization of the harmonic suppression process based on actual suppression effectiveness. The dynamic setting of the harmonic suppression benchmark and the gradual adjustment of the suppression signal are repeatedly executed until the harmonic characteristic parameters meet the preset convergence criteria. This achieves continuous optimization and control of harmonic interference, ensuring that the harmonic components on the DC bus side are ultimately suppressed within a reasonable range. This guarantees the normal operation of power electronic equipment, control devices, sensors, and other components within the flywheel energy storage system, reducing problems such as control signal distortion, abnormal speed regulation, and false triggering of protection actions caused by harmonic interference. It extends the service life of all equipment within the system, improves the operational reliability and energy conversion efficiency of the entire flywheel energy storage system, and enables the system to maintain stable performance under high-power, high-speed operating conditions. This further expands the application potential of flywheel energy storage systems in scenarios such as power system frequency and voltage regulation and new energy consumption. Attached Figure Description

[0017] Figure 1 This is a schematic diagram illustrating the working principle of the flywheel energy storage-based harmonic conduction interference suppression method described in this invention. Figure 2 A flowchart for the frequency domain decomposition of current and voltage signals; Figure 3 A flowchart for generating the speed compensation coefficient; Figure 4 A flowchart of the chain-like inhibition conduction mechanism; Figure 5 A flowchart for re-determining the harmonic suppression reference point. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Please see Figure 1 This invention provides a method for suppressing harmonic conducted interference based on flywheel energy storage, the method comprising: By acquiring current and voltage signals from the DC bus side of the flywheel energy storage system in real time, frequency domain decomposition is performed to separate the fundamental and harmonic components. Current and voltage harmonic characteristic parameters are calculated based on the harmonic components. A preset harmonic threshold condition is compared with the harmonic characteristic parameters to dynamically set a harmonic suppression benchmark point. A progressive harmonic suppression signal is injected at the benchmark point, and the rate of change of suppression intensity is adjusted by a slope control module. A speed compensation coefficient is generated based on the coupling relationship between the harmonic characteristic parameters and the flywheel rotor speed, and this coefficient is used to adjust the slope of the progressive harmonic suppression signal in real time. The adjusted progressive harmonic suppression signal is diffused from a single point injection to the entire flywheel energy storage system through a chain-like suppression conduction mechanism. The harmonic suppression feedback of the current and voltage signals is monitored in real time, and the harmonic threshold condition is updated based on the feedback. The dynamic setting of the harmonic suppression benchmark point and the adjustment of the progressive harmonic suppression signal are repeated until the harmonic characteristic parameters meet the preset convergence criteria.

[0020] Example 1: See Figure 2 In the actual operation of flywheel energy storage systems, the current and voltage signals on the DC bus side are distorted due to the high-speed switching action of the power converter, sudden load changes, and the nonlinear characteristics of the flywheel motor itself. These distorted signals not only contain basic power frequency components but also a variety of high-frequency harmonic components. These harmonic components propagate within the system through conduction and coupling, potentially affecting the stability of the control system and even interfering with the power quality of the grid. Therefore, accurate frequency domain decomposition of the current and voltage signals to separate and identify these harmonic components is the starting point and key data source for the entire suppression method.

[0021] Signal acquisition is accomplished using high-precision Hall current sensors and differential voltage sensors, which are directly mounted or connected to the positive and negative buses of the DC bus. The sensors continuously capture instantaneous values ​​of current and voltage at a fixed, sufficiently high sampling frequency. The acquired analog signals are processed by an anti-aliasing filter, then converted into a digital signal sequence by a high-speed analog-to-digital converter, and finally fed into a digital signal processor or a dedicated field-programmable gate array for further processing.

[0022] The core of frequency domain decomposition is the use of the Fast Fourier Transform (FFT) algorithm. This algorithm can transform a discrete signal sequence in the time domain into the frequency domain, clearly showing which frequencies, amplitudes, and phases of the sine waves constitute the signal. For current signals, the processor first loads the data within the current sampling window into memory. To reduce spectral leakage caused by signal truncation, a window function, such as a Hanning or Hamming window, is applied to the data before the transformation. The window function weights the data at both ends of the sampling window, smoothly transitioning it to zero, thereby improving the accuracy of frequency resolution.

[0023] After windowing preprocessing, the Fast Fourier Transform (FFT) program begins execution. It decomposes the time-domain current signal into a series of complex frequency components. Each frequency component corresponds to a frequency point, its magnitude represents the amplitude of that component, and its argument represents the phase information. After the transform, the program identifies the fundamental component with the largest amplitude (usually the 50Hz or 60Hz power frequency component). All other frequency components, whether lower or higher than the fundamental frequency, are classified as harmonic components as long as their frequency is an integer multiple of the fundamental frequency. These harmonic components are separated from the complete spectrum. For voltage signals, the identical process described above is executed synchronously: the same sampling window, the same window function, and the same FFT algorithm, ultimately separating the fundamental voltage component and the voltage harmonic components.

[0024] The separated current harmonic component data stream contains rich information. The extraction process focuses on characteristic harmonics, such as the 5th, 7th, 11th, and 13th harmonics. For each harmonic of interest, the program records its frequency value, calculates its percentage relative to the fundamental frequency amplitude (i.e., harmonic content), and precisely records its phase angle. All this information together constitutes the current harmonic characteristic parameters. This is a dynamic dataset that is continuously updated as the system's operating state changes. Similarly, the amplitude, content, and phase information extracted from the voltage harmonic components constitute the voltage harmonic characteristic parameters.

[0025] These two sets of characteristic parameters are updated in real time and stored in a circular buffer. They not only clearly quantify the severity of harmonic pollution in the current system, but more importantly, their amplitude directly indicates the strength of harmonic energy, while their phase information reveals the polarity of the harmonics and the possible interactions between different harmonic sources. For example, a sudden change in the phase of a specific harmonic may indicate a change in the state of a power switching element in the system. The entire frequency domain decomposition and characteristic parameter generation process begins processing the next window immediately after one sampling window is completed, forming a continuous, real-time monitoring data stream. This provides indispensable and accurate input for subsequent threshold judgment, suppression reference point selection, and suppression signal generation. The stability and accuracy of this process directly affect the response speed and final effect of the entire harmonic suppression system.

[0026] Example 2: During the operation of a flywheel energy storage system, the dynamic changes in harmonic characteristic parameters directly reflect the real-time status of the system's internal power quality. These parameters are not static data, but fluctuate continuously with changes in flywheel speed, load demand, and power converter switching frequency. The process of dynamically setting harmonic suppression benchmarks is essentially an intelligent decision-making process based on real-time data and preset threshold values. Its purpose is to accurately allocate limited suppression resources to the system nodes that most require intervention, thereby achieving efficient and targeted harmonic mitigation.

[0027] The first, second, and third harmonic thresholds are set in the control system based on the safe operation specifications of the flywheel energy storage system, the equipment's tolerance capabilities, and the requirements for grid-connected power quality. These thresholds can be fixed values ​​or range values ​​that are allowed to fluctuate within a certain range. They constitute the objective criteria for determining whether the system needs harmonic intervention.

[0028] The system continuously monitors the current harmonic characteristic parameters and voltage harmonic characteristic parameters transmitted from the frequency domain decomposition module. When the monitoring logic detects that a current harmonic characteristic parameter, such as the content of a specific harmonic or the total harmonic distortion rate, continuously and significantly exceeds the limit range of the first harmonic threshold, the control core makes a decision: to set the flywheel power conversion unit node where the current exceedance phenomenon is detected as the first harmonic suppression reference point. The power conversion unit is the interface for energy exchange between the flywheel and the DC bus, and its nodes typically contain switching devices such as IGBTs or MOSFETs, which are a major source of current harmonics. Setting this node as the reference point means that the suppression action will directly act on the vicinity of the harmonic source.

[0029] If the excessive parameter is a voltage harmonic characteristic parameter, such as the harmonic distortion rate of the bus voltage exceeding the second harmonic threshold, the control logic will determine to set the current flywheel bus connection node as the second harmonic suppression reference point. The bus connection node is a critical point for the collection and distribution of system power, and voltage quality is paramount here. Setting a reference point here helps stabilize the voltage waveform of the entire bus and prevents harmonic voltages from affecting other parallel-operating equipment.

[0030] When the control system detects that the harmonic characteristic parameters of both current and voltage simultaneously exceed the third harmonic threshold, it often indicates that the harmonic disturbance is no longer a local phenomenon and may have triggered systemic oscillations or the superposition effect of multiple harmonic sources. In this case, the control system will escalate its response level, setting the central control node of the flywheel energy storage system as the primary harmonic suppression reference point. This node possesses the most global system view and the highest control authority, aiming to coordinate global suppression actions.

[0031] Once the reference points are set, the corresponding suppression signal injection mechanism is immediately activated. At the first harmonic suppression reference point (power conversion unit node), a first-type progressive harmonic suppression signal is injected. This signal is designed to specifically cancel or weaken current harmonics generated at this node. At the second harmonic suppression reference point (bus connection node), a second-type progressive harmonic suppression signal is injected, with its waveform and phase adjusted to compensate for bus voltage distortion. At the main harmonic suppression reference point (central control node), a global progressive harmonic suppression signal is injected. This is a comprehensive compensation signal designed to quell harmonic disturbances at the system level.

[0032] None of these suppression signals are injected instantaneously at maximum intensity, as that could cause system shock. They are all "gradual." Each type of signal has its initial suppression intensity change rate adjusted by an independent slope control module. This module controls the suppression signal to start from zero, with its amplitude or energy gradually increasing at a preset, relatively gentle slope. This initial change rate setting takes into account the system's inertia and the response time of the control loop, aiming to allow the suppression action to be smoothly integrated into the system and avoid new instability caused by sudden strong intervention. Through this on-demand setting, classified injection, and gradual start-up method, harmonic suppression can be carried out efficiently and smoothly.

[0033] Example 3: See Figure 3The dynamic characteristics of flywheel energy storage systems determine an inherent coupling relationship between their harmonic behavior and rotor speed. Changes in rotor speed directly affect the back electromotive force characteristics of the flywheel motor windings, the modulation strategy of the power converter, and the system's equivalent impedance network, thus causing changes in the amplitude and phase characteristics of harmonic components. This coupling effect means that a harmonic suppression strategy effective at a specific speed may become less effective or even counterproductive after the speed changes. Therefore, it is necessary to introduce a compensation mechanism that can reflect the degree of harmonic impact of speed changes in real time, and apply this compensation amount to the control loop of the suppression signal to achieve adaptive harmonic suppression.

[0034] The generation of the speed compensation coefficient is a continuous data fusion and calculation process. The system acquires the current speed value of the flywheel rotor in real time through a high-resolution encoder mounted on the flywheel rotor. This value is read and updated at a constant sampling period. At the same time, the current harmonic characteristic parameters and voltage harmonic characteristic parameters continuously output from the frequency domain decomposition module are also acquired synchronously. These characteristic parameters are a quantitative representation of the harmonic activity intensity.

[0035] To establish a quantitative correlation between rotational speed and harmonic intensity, the calculation process multiplies and couples the harmonic characteristic parameters with the rotational speed value. Specifically, the current harmonic characteristic parameter is multiplied by the current rotational speed of the flywheel rotor, and the product is defined as the first rotational speed coupling factor. This factor comprehensively reflects the overall activity level of the current harmonics at the current rotational speed. Similarly, the voltage harmonic characteristic parameter is multiplied by the current rotational speed of the same flywheel rotor, and the product is defined as the second rotational speed coupling factor, which characterizes the voltage harmonic activity level at the current rotational speed. The first and second rotational speed coupling factors describe the coupling effect between rotational speed and harmonics from the perspectives of current and voltage, respectively. To obtain a comprehensive single index representing the overall harmonic-rotational coupling state of the system, the arithmetic mean of these two factors is used as the final rotational speed compensation coefficient. The calculation of this coefficient can be expressed as:

[0036] in: The speed compensation coefficient is a dimensionless scaling factor. Representative parameters of current harmonic characteristics, such as total harmonic distortion expressed as a percentage; These represent voltage harmonic characteristic parameters, also expressed as percentages. This represents the current rotational speed of the flywheel rotor, in radians per second. This coefficient... The value will change dynamically with the fluctuations in rotational speed and harmonic level.

[0037] Speed ​​compensation coefficient was generated Subsequently, its core function lies in real-time adjustment of the slope control module for the three types of progressive harmonic suppression signals. The slope control module originally had an initial suppression intensity change rate preset, which determined how quickly the suppression signal amplitude increased. However, this preset value was set based on a typical operating condition of the system and did not consider the impact of speed changes. The coefficients are input into the independent slope control modules for the first type, the second type, and the global progressive harmonic suppression signals, respectively. Within each module, As a multiplicative factor, the rate of change of the initial inhibition intensity is scaled proportionally. The specific scaling relationship is linear: when... When the value increases, it indicates that harmonic activity is more significant at the current high speed, requiring a faster suppression response. Therefore, the actual suppression intensity change rate output by the slope control module will increase proportionally, causing the suppression signal intensity to rise with a steeper slope, thereby accelerating the suppression process. Conversely, when... When the value decreases, it indicates that the harmonic threat is relatively low under the current operating conditions, and the rate of increase in suppression intensity will slow down proportionally, employing a more gentle intervention method to avoid overcompensation. This process is continuous. In each control cycle, the speed value and harmonic characteristic parameters are resampled. The signal is recalculated and immediately used to update the gain of the three slope control modules. This ensures that the rate of change of the harmonic suppression signal intensity always matches the real-time operating state of the flywheel system (the combined state of speed and harmonics), guaranteeing the dynamic accuracy of the suppression action and enabling the entire system to adapt to the harmonic suppression requirements under various operating conditions of the flywheel, from high speed to low speed.

[0038] Example 4: See Figure 4 In flywheel energy storage systems, harmonic suppression is not an independent behavior of isolated nodes, but a process that requires global coordination. The core idea of ​​the chain-like suppression transmission mechanism is to orderly transmit and synchronize the suppression action initiated at a key node to other relevant nodes through the inherent communication network within the system, thereby forming a coordinated and global suppression posture and preventing imbalances or new disturbances that may be caused by local suppression.

[0039] This mechanism sets different information transmission paths based on different types of harmonic suppression reference points. When a flywheel power conversion unit node is set as the first harmonic suppression reference point and begins injecting the first type of progressive harmonic suppression signal, the control system of that node packages its current "harmonic suppression state quantity." This state quantity is a data packet, which contains not only the type of suppression signal currently injected by the node (first type) and the real-time absolute value of the suppression intensity, but more importantly, the actual suppression intensity change rate parameter after adjustment by the speed compensation coefficient, as well as the effective range identifier of the suppression signal. This data packet is not sent indiscriminately to all nodes, but is precisely transmitted through point-to-point communication to the "adjacent flywheel power conversion unit node" with which it is most closely electrically connected and most likely to be affected by its harmonics.

[0040] When a flywheel bus connection node is set as the second harmonic suppression reference point, it generates its own harmonic suppression status data packet, which contains detailed information about the second type of suppression signal. This data packet is then sent to other directly connected "adjacent flywheel bus connection nodes." For the central control node set as the primary harmonic suppression reference point, its generated global harmonic suppression status data packet contains parameters of the global suppression signal and system-level coordination commands. This data packet is broadcast to all flywheel energy storage subsystem nodes in the network to ensure that the highest-level commands are received by all nodes.

[0041] Upon receiving harmonic suppression state quantities from the reference point, neighboring nodes do not simply copy their suppression parameters; instead, they initiate a synchronization update process. Each node has a built-in suppression signal parameter update logic. This logic parses the received state quantities, extracts key parameters, particularly the rate of change of suppression intensity. Then, based on local harmonic characteristic parameter measurements and its role in the system, it makes corresponding and coordinated adjustments to its own progressive harmonic suppression signal parameters. For example, a neighboring power conversion unit node receiving a Type I suppression state quantity might adjust the rate of change of its prepared or injected suppression signal according to the received rate of change parameter, ensuring that the suppression actions of multiple nodes are coordinated in intensity and rhythm, avoiding cancellation effects or new harmonics due to inconsistent timing.

[0042] Throughout the suppression process, the system continuously monitors the feedback effect of harmonic suppression. This is achieved by calculating the decrease rate of current harmonic characteristic parameters and voltage harmonic characteristic parameters in real time. The decrease rate reflects how quickly the harmonic level decreases over time after the suppression action begins, and is a direct indicator of the dynamic response of the suppression effect. The calculated current harmonic decrease rate is defined as the current harmonic suppression feedback quantity, and the voltage harmonic decrease rate is defined as the voltage harmonic suppression feedback quantity.

[0043] These feedback values ​​are fed into a threshold update logic module, which presets an update threshold representing an acceptable minimum feedback efficiency threshold. The system observes the continuous performance of these feedback values. For example, if the current harmonic suppression feedback value remains below the preset update threshold for several consecutive monitoring cycles, it indicates that the currently set first and third harmonic thresholds may be too sensitive, causing suppression actions to be frequently triggered even when harmonic levels are not severe, or that the suppression effect fails to reach the expected rate. In this case, the update logic will decide to raise the trigger thresholds for the first and third harmonic thresholds. This means that the system raises the "threshold" for current harmonic tolerance, requiring higher current harmonic levels in the future to trigger the setting of the suppression benchmark. Similarly, if the voltage harmonic suppression feedback value remains low, the trigger thresholds for the second and third harmonic thresholds will also be raised accordingly.

[0044] This threshold increase is an adaptive optimization process, with increments typically cautious and gradual to avoid the system missing necessary intervention opportunities. Table 1 illustrates the correspondence between the harmonic suppression feedback and the resulting dynamic adjustment of the harmonic threshold over a series of observation periods.

[0045] Table 1: Correspondence between Harmonic Suppression Feedback Amount and Threshold Adjustment .

[0046] Spatial coordination achieved through chain transmission and temporal adaptation achieved through feedback monitoring together constitute a harmonic suppression system for a large flywheel energy storage system that is continuously optimized in both spatiotemporal dimensions.

[0047] Example 5: See Figure 5 Harmonic suppression in flywheel energy storage systems is a dynamic, cyclical, and progressive process, rather than a one-off, permanent action. This is because the system's operating conditions, load status, and the flywheel's rotational speed are constantly changing. The previously set harmonic suppression benchmark may no longer be optimal due to these changes, or the previously set harmonic threshold conditions may require a reassessment of the entire system's monitoring status after adaptive adjustments. Therefore, repeatedly resetting the dynamic harmonic suppression benchmark is the core mechanism for maintaining long-term effectiveness in suppression.

[0048] This iterative process relies heavily on real-time updated harmonic threshold conditions. These thresholds, including the first, second, and third harmonic thresholds, have been raised or possibly lowered in previous suppression cycles based on actual suppression feedback. The system control core now uses these new, optimized thresholds as the basis for a complete system scan and diagnostic. It continuously collects the latest current and voltage harmonic characteristic parameters and compares this real-time data with the updated first harmonic thresholds. If the current harmonic level at a flywheel power conversion unit node still exceeds this new, potentially higher, threshold, that node is re-established as the first harmonic suppression reference point; conversely, if its harmonic level is below the new threshold, its reference point status is revoked, and the corresponding suppression signal injection is stopped, thereby freeing up system resources.

[0049] The exact same re-judgment logic is synchronously applied to bus connection nodes. The system compares the latest voltage harmonic characteristic parameters with the updated second harmonic threshold to determine whether to re-set or retain a bus connection node as a second harmonic suppression reference point. For the central control node's status as the primary reference point, the judgment criteria are the most stringent. It requires checking whether both current and voltage harmonic characteristic parameters still exceed the limits based on the updated third harmonic threshold, thus determining whether to initiate or maintain global coordinated suppression actions. This "monitoring-comparison-judgment-setting" cycle repeats continuously, allowing the distribution of harmonic suppression reference points to dynamically map the system's current actual harmonic "hotspot" distribution, ensuring that suppression actions always precisely target the areas most in need of intervention.

[0050] The ultimate goal of the entire harmonic suppression process is to converge the system's harmonic level to a predetermined, acceptable stable state. Whether this goal is achieved is not determined by a single measurement, but by a rigorous set of convergence criteria. This criterion examines the system's stability from multiple dimensions. First, it requires that the measured values ​​of the current harmonic characteristic parameters be below the first convergence threshold for three consecutive sampling periods. These three sampling periods cannot be instantaneous but must span a certain time range to prove that the reduction in current harmonics is not a random fluctuation but a continuous improvement. Similarly, the voltage harmonic characteristic parameters must also meet the condition that the measured values ​​are below the second convergence threshold for three consecutive periods, proving that the voltage quality has been steadily improved.

[0051] The convergence criterion continuously monitors the ratio of current harmonic characteristic parameters to voltage harmonic characteristic parameters. This ratio reflects the interaction between harmonic currents and harmonic voltages in the system. The criterion requires that this ratio must be stably maintained within a preset range, without large-amplitude or periodic oscillations. This condition ensures that harmonic suppression not only reduces the amplitude to a certain level, but more importantly, restores a balance between harmonic components in the system, eliminating potential resonance or instability risks.

[0052] Only when the current harmonics remain consistently below the threshold, the voltage harmonics remain consistently below the threshold, and the harmonic ratio remains stable, will the control system ultimately determine that the harmonic suppression process is complete and the system has entered steady-state operation mode. At this point, all progressive harmonic suppression signals will either enter a maintenance state or smoothly exit according to a predetermined program. However, the system's monitoring function remains active, ready to initiate a new round of dynamic suppression cycles if the harmonic level exceeds the limit again. This design enables the flywheel energy storage system to have adaptive harmonic mitigation capabilities to cope with various operating condition changes during long-term operation.

[0053] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0054] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A flywheel energy storage based harmonic conducted interference suppression method, characterized in that, The method comprises the following steps: real-time acquisition of current signal and voltage signal on the DC bus side of the flywheel energy storage system; frequency domain decomposition of the current signal and the voltage signal to separate the fundamental component and the harmonic component; calculation of harmonic characteristic parameters from the harmonic component, including current harmonic characteristic parameters and voltage harmonic characteristic parameters; comparison of the harmonic threshold condition with the harmonic characteristic parameters to dynamically set the harmonic suppression reference point; injection of gradual harmonic suppression signal at the harmonic suppression reference point, the gradual harmonic suppression signal being adjusted by a slope control module to change the suppression intensity; calculation of the rotational speed compensation coefficient according to the coupling relationship between the harmonic characteristic parameters and the rotational speed of the flywheel rotor; real-time adjustment of the slope of the gradual harmonic suppression signal by using the rotational speed compensation coefficient; diffusion of the adjusted gradual harmonic suppression signal from single-point injection to the whole flywheel energy storage system through a chain suppression conduction mechanism; real-time monitoring of the harmonic suppression feedback of the current signal and the voltage signal, and updating of the harmonic threshold condition according to the harmonic suppression feedback; repeated execution of the dynamic setting of the harmonic suppression reference point and the adjustment of the gradual harmonic suppression signal until the harmonic characteristic parameters meet the preset convergence criterion.

2. The method of claim 1, wherein, The frequency domain decomposition of the current signal and the voltage signal comprises the following steps: decomposition of the current signal into current fundamental component and current harmonic component by using fast Fourier transform; synchronous decomposition of the voltage signal into voltage fundamental component and voltage harmonic component by using fast Fourier transform; extraction of the amplitude and phase information of the current harmonic component to generate current harmonic characteristic parameters; extraction of the amplitude and phase information of the voltage harmonic component to generate voltage harmonic characteristic parameters.

3. The method of claim 2, wherein, The dynamic setting of the harmonic suppression reference point comprises the following steps: when the current harmonic characteristic parameters exceed the first harmonic threshold, the current flywheel power conversion unit node is set as the first harmonic suppression reference point; when the voltage harmonic characteristic parameters exceed the second harmonic threshold, the current flywheel bus connection node is set as the second harmonic suppression reference point; when the current harmonic characteristic parameters and the voltage harmonic characteristic parameters exceed the third harmonic threshold, the flywheel energy storage system central control node is set as the main harmonic suppression reference point.

4. The method of claim 3, wherein, The injection of gradual harmonic suppression signal at the harmonic suppression reference point comprises the following steps: injection of the first type of gradual harmonic suppression signal at the first harmonic suppression reference point; injection of the second type of gradual harmonic suppression signal at the second harmonic suppression reference point; injection of the global gradual harmonic suppression signal at the main harmonic suppression reference point; the first type of gradual harmonic suppression signal, the second type of gradual harmonic suppression signal and the global gradual harmonic suppression signal are adjusted by independent slope control modules to change the initial suppression intensity.

5. The method of claim 4, wherein, The generation of the rotational speed compensation coefficient comprises the following steps: real-time acquisition of the current rotational speed value of the flywheel rotor; calculation of the product of the current harmonic characteristic parameters and the current rotational speed value of the flywheel rotor to generate the first rotational speed coupling factor; calculation of the product of the voltage harmonic characteristic parameters and the current rotational speed value of the flywheel rotor to generate the second rotational speed coupling factor; An arithmetic mean of the first rotational speed coupling factor and the second rotational speed coupling factor is taken as a rotational speed compensation coefficient.

6. The method of claim 5, wherein, The real-time adjustment of the slope of the progressive harmonic suppression signal using the rotational speed compensation coefficient comprises: The rotational speed compensation coefficient is input into a slope control module of a first type of progressive harmonic suppression signal to scale an initial suppression intensity change rate; The rotational speed compensation coefficient is input into a slope control module of a second type of progressive harmonic suppression signal to scale an initial suppression intensity change rate; The rotational speed compensation coefficient is input into a slope control module of a global progressive harmonic suppression signal to scale an initial suppression intensity change rate.

7. The method of claim 6, wherein, The chain suppression conduction mechanism comprises: The harmonic suppression state quantity of the first harmonic suppression reference point is transmitted to an adjacent flywheel power conversion unit node; The harmonic suppression state quantity of the second harmonic suppression reference point is transmitted to an adjacent flywheel bus connection node; The harmonic suppression state quantity of the main harmonic suppression reference point is broadcast to all flywheel energy storage subsystem nodes; The progressive harmonic suppression signal parameters are synchronously updated between adjacent nodes according to the harmonic suppression state quantity.

8. The method of claim 7, wherein, The updating of the harmonic threshold conditions according to the harmonic suppression feedback quantity comprises: A current harmonic suppression feedback quantity is generated by real-time calculation of a descending rate of the current harmonic characteristic parameter; A voltage harmonic suppression feedback quantity is generated by real-time calculation of a descending rate of the voltage harmonic characteristic parameter; When the current harmonic suppression feedback quantity continuously falls below a preset update threshold, the trigger thresholds of the first harmonic threshold and the third harmonic threshold are raised; When the voltage harmonic suppression feedback quantity continuously falls below a preset update threshold, the trigger thresholds of the second harmonic threshold and the third harmonic threshold are raised.

9. The method of claim 8, wherein, The repeated execution of the dynamic setting of the harmonic suppression reference point comprises: Whether a power conversion unit node is set as a first harmonic suppression reference point is re-determined according to the updated first harmonic threshold; Whether a bus connection node is set as a second harmonic suppression reference point is re-determined according to the updated second harmonic threshold; Whether a central control node is set as a main harmonic suppression reference point is re-determined according to the updated third harmonic threshold.

10. The method of claim 9, wherein, The convergence criterion comprises: The current harmonic characteristic parameter is continuously sampled three times and each value is below a first convergence threshold; The voltage harmonic characteristic parameter is continuously sampled three times and each value is below a second convergence threshold; The ratio of the current harmonic characteristic parameter to the voltage harmonic characteristic parameter is stably maintained in a preset interval.

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