A method and system for resonance suppression of shunt capacitors

Abstract

The application discloses a resonance suppression method and system of a parallel capacitor, which is applied to a parallel capacitor topology circuit, and the parallel capacitor topology circuit comprises at least two capacitor sub-zones connected in parallel, a switchable damping branch and a discharge branch. The resonance suppression method comprises the following steps: collecting bus voltage, bus total current and sub-zone currents of the at least two capacitor sub-zones; performing band-pass analysis on the collected signals to obtain various indexes representing resonance states; constructing a resonance risk coefficient according to the various indexes and comparing the resonance risk coefficient with hierarchical threshold values to output hierarchical suppression instructions; when the resonance risk coefficient reaches preset conditions, executing a pre-warning, a resonance suppression action and a fault isolation action in a predetermined order; and when the resonance risk coefficient is continuously lower than a recovery threshold value for a preset time and the bus voltage, the bus total current, the sub-zone currents and the temperature rise of a connection point meet recovery conditions, the resonance suppression state is exited. The application has the advantages that short-time disturbances and continuous resonances can be distinguished in time, and resonances can be effectively suppressed.

Description

Technical Field

[0001] This invention relates to the field of high-power power electronics and power capacitor protection technology, specifically to a method and system for suppressing resonance in parallel capacitors. Background Technology

[0002] In high-power converters, pulse power supplies, energy storage converters, and high-voltage DC support circuits, multiple large-capacity power capacitors are often connected in parallel to form a capacitor bank in the mF range. Since the capacitor body, capacitor leads, busbars, connecting copper busbars, and device packaging inevitably introduce nH-level stray inductance, and each branch and connection interface also has mΩ-level distributed resistance and device resistance, the entire system can be equivalent to a low-damped RLC network in engineering terms.

[0003] When the system is subjected to switching harmonics, periodic pulsating currents, or topology reconfiguration disturbances, the aforementioned low-damped RLC network will exhibit significant equivalent series resonance or low-impedance resonance in the 500–2000 Hz frequency band under certain operating conditions. Once resonance is established, problems such as amplified bus current, increased temperature rise at connection interfaces, increased amplitude of capacitor terminal voltage oscillations, localized overheating, and accelerated capacitor lifespan degradation are likely to occur. These problems are particularly pronounced in high-power systems with a rated voltage of approximately 3500 V and a total current of approximately 50 kA.

[0004] Existing protection schemes typically focus on overcurrent, overvoltage, overtemperature, or absolute value alarms. For example, the relay protection method and device for detuning faults in LC parallel circuits disclosed in Chinese patent application publication number CN104113045A focuses on absolute value alarms, which often only passively activate when the oscillation amplitude is already large, making it difficult to distinguish between short-term disturbances and continuous resonance in a timely manner. Summary of the Invention

[0005] The technical problem to be solved by the present invention is that the existing technology reacts passively when the oscillation amplitude is already large, and it is difficult to distinguish between short-term disturbances and continuous resonance in time, thus making it difficult to effectively suppress resonance.

[0006] This invention solves the above-mentioned technical problems through the following technical means: a resonance suppression method for parallel capacitors, applied to a parallel capacitor topology circuit, wherein the parallel capacitor topology circuit includes at least two capacitor partitions connected in parallel, a switchable damping branch, and a discharge branch, and the resonance suppression method includes:

[0007] S1. Collect bus voltage, total bus current, and current of at least two capacitor banks; S2. Perform bandpass analysis on the acquired signal to obtain various indicators characterizing the resonance state; S3. Construct a resonance risk coefficient based on various indicators and compare it with the graded threshold, then output a graded suppression command; when the resonance risk coefficient reaches the preset condition, execute the warning, resonance suppression, and fault isolation actions in a predetermined order; when the resonance risk coefficient continuously reaches the preset condition, execute the warning, resonance suppression, and fault isolation actions in a predetermined order. Time below recovery threshold Furthermore, the bus voltage, total bus current, current in each zone, and temperature rise at connection points are all continuous. When the time remains within the allowable range, the system is determined to meet the recovery exit condition and exits the resonance suppression state.

[0008] Furthermore, the switchable damping branch is an energy-consuming branch formed by connecting a resistor, an RC branch, or an RL branch in series with the switching unit.

[0009] Furthermore, the discharge branch is a branch formed by a switching unit connected in series with a resistor.

[0010] Furthermore, each capacitor bank consists of multiple power capacitors connected in parallel, and a corresponding switching unit is set on the branch where each capacitor bank is located.

[0011] Further, S2 includes: Bandpass analysis was performed on the collected signals in the 500–2000 Hz frequency band to obtain the resonance amplitude index, growth rate index, and damping index, which characterize the resonance state.

[0012] Furthermore, the damping index is calculated using the logarithmic decrease rate of adjacent oscillation peaks, the bandpass impedance phase offset, the equivalent damping ratio, or a weighted combination thereof.

[0013] Furthermore, the resonance risk coefficient is calculated as follows: Calculate the resonance amplitude index ,in, These are the voltage-mode resonant amplitudes. Current-mode resonant amplitude , zone resonance amplitude and zone current differences The weighting coefficients, and satisfying , , , , These are normalized indices for voltage-mode resonance amplitude, current-mode resonance amplitude, zone resonance amplitude, and zone current difference, respectively. growth rate indicators The value is obtained based on the amplitude change in adjacent sampling periods. Growth rate index within a sampling window

[0014] in, For the first The resonance amplitude index within each sampling window It is a positive number; Damping index , This represents the logarithmic decrease rate between adjacent oscillation peaks and , Indicates the first bandpass signal The amplitude of each oscillation peak; Resonance risk coefficient ,in, , , All are weighted coefficients. This represents the reference value for the resonance amplitude. This represents a reference value for the growth rate. This indicates the damping reference value.

[0015] Furthermore, S3 includes: when At that time, the system continues to operate normally. To restore the threshold; when When this occurs, the system enters an early warning state, records the resonant frequency, resonant amplitude, and zonal distribution, and outputs an alarm signal to the host computer. This is the first-order inhibition threshold; when hour, To reach the fault isolation threshold, the system enters Level 1 suppression mode. First, the switchable damping branch is engaged. After engaging the switchable damping branch, the resonance suppression system enters the Level 1 suppression observation phase. If, during the Level 1 suppression observation phase... continuous Time higher or growth rate indicators continuous Time exceeds the set growth rate threshold If the first-level suppression is insufficient, the second-level suppression action is executed. The second-level suppression action includes cutting off at least one capacitor section, reducing the equivalent capacitance, changing the connection status of the parallel branch, and sending a control command to the upstream converter to weaken the excitation source. like Greater than or equal to ,or Higher than And the resonant state is maintained continuously for more than If any one of the following exceeds the safety limit: bus voltage, bus total current, or connection point temperature rise, then a fault isolation action shall be immediately performed. The fault isolation action includes disconnecting the main circuit, cutting off the resonant contribution zone, and starting the discharge branch. when continuous Time below recovery threshold Furthermore, the bus voltage, total bus current, current in each zone, and temperature rise at connection points are all continuous. When the time remains within the allowable range, the resonance suppression system first maintains the current capacitor partition connection state. After a certain time, the switchable damping branch is disconnected, and then the removed capacitor sections are restored step by step in a preset order. After each removed capacitor section is restored, if... Within a time The recovery threshold was not exceeded again. And voltage-mode resonance amplitude Below the allowable bandwidth of the bus voltage Current-mode resonant amplitude Below the allowable bandwidth of the total bus current , zone resonance amplitude Below the zone's allowable band current amplitude And the temperature rise at the connection point Below the temperature rise limit If so, continue to restore the next cut capacitor partition; if Exceeding the recovery threshold again If the condition is not met, the recovery process will stop and the process will re-enter the resonance suppression judgment process.

[0016] Furthermore, the aforementioned The value range is 20ms to 200ms. The value range is 0.2s to 2s. The value range is 0.5s to 10s. The value range is 0.5s to 5s, the aforementioned The value range is 0.2s to 2s.

[0017] The present invention also provides a resonance suppression system for parallel capacitors, which implements the resonance suppression method described above and is applied to a parallel capacitor topology circuit. The parallel capacitor topology circuit includes at least two capacitor partitions connected in parallel, a switchable damping branch, and a discharge branch. The resonance suppression system includes: The signal acquisition module is used to acquire bus voltage, total bus current, and zone current of at least two capacitor banks; The frequency band analysis module is used to perform bandpass analysis on the acquired signal to obtain various indicators characterizing the resonance state. The criterion decision module is used to construct a resonance risk coefficient based on various indicators and compare it with the graded threshold, and output graded suppression instructions. The execution module is used to perform early warning, resonance suppression, and fault isolation actions in a predetermined sequence when the resonance risk coefficient reaches a preset condition; when the resonance risk coefficient continuously... Time below recovery threshold Furthermore, the bus voltage, total bus current, current in each zone, and temperature rise at connection points are all continuous. When the time remains within the allowable range, the system is determined to meet the recovery exit condition and exits the resonance suppression state.

[0018] The advantages of this invention are: (1) The present invention calculates the resonance risk coefficient based on various indicators characterizing the resonance state, compares the resonance risk coefficient with the graded threshold, outputs graded suppression instructions, and executes early warning, resonance suppression and fault isolation actions in a predetermined order. It can identify resonance risks in advance and implement protection strategies of recoverable suppression and necessary isolation according to risk level, distinguish between short-term disturbances and continuous resonance in a timely manner, and effectively suppress resonance.

[0019] (2) Although the existing fixed damping scheme can reduce the amplitude to a certain extent, it will introduce additional losses in the long term, reduce efficiency and increase the thermal design burden. The present invention avoids the introduction of additional losses in the long term and reduces the thermal design burden by switching the damping.

[0020] (3) The present invention can identify and suppress resonance before the formation of overcurrent and overvoltage peaks, and can change the equivalent parameters of the system by switching damping and partition decapacitation to improve the equivalent damping and shift the resonance point; it can prioritize the implementation of graded suppression without immediately shutting down the whole machine, taking into account both safety and continuous operation capability; it can exit the suppression state according to hysteresis logic after the resonance disappears, avoiding frequent oscillating switching.

[0021] (4) This invention collects bus voltage, total bus current, and partition current of at least two capacitor banks. The bus voltage signal can reflect whether the capacitor terminal voltage has started to oscillate in a specific frequency band; the total bus current can reflect whether the entire parallel capacitor bank has a resonant current amplification trend; and the partition current can reflect whether there is abnormal current distribution and local circulating current between different capacitor banks. After the above signals are analyzed in the target frequency band, the system can determine whether the oscillation is concentrated in the frequency band where the parallel capacitor bank is prone to resonance, rather than just judging the magnitude of the instantaneous current and instantaneous voltage. Thus, the overall scheme can identify and suppress resonance before the overcurrent and overvoltage peaks are formed.

[0022] (5) Short-term disturbances and continuous resonances differ significantly in duration, frequency stability, amplitude variation trend, damping performance, and zoned current distribution. Short-term disturbances are usually caused by transient processes such as switching actions, load abrupt changes, and topology switching. Continuous resonances are usually characterized by the repeated occurrence of oscillation components within a certain frequency band, with a relatively stable frequency. This invention avoids direct triggering of strong protection actions by setting a duration criterion. Only when the resonance characteristics exist continuously within a preset time, and multiple conditions such as amplitude, growth trend, and damping state are simultaneously met, will the system enter the warning, first-level suppression, or second-level suppression state. This can avoid misjudgment caused by occasional spikes, sampling glitches, and switching transients, and effectively distinguish between short-term disturbances and continuous resonances. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the structure of a parallel capacitor resonance suppression system disclosed in an embodiment of the present invention; Figure 2 This is a flowchart of a method for suppressing resonance in a parallel capacitor as disclosed in an embodiment of the present invention; Figure 3 This is a schematic diagram of resonance suppression based on switchable damping branches and partitioned decapacitance in a parallel capacitor resonance suppression method disclosed in an embodiment of the present invention. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, 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.

[0025] Example 1 like Figure 1The present invention provides a resonance suppression system for parallel capacitors, applied to a parallel capacitor topology circuit. The parallel capacitor topology circuit includes a positive main busbar, a negative main busbar, at least two capacitor banks connected in parallel between the positive and negative main busbars, a switching unit, a switchable damping branch connected in parallel with the capacitor banks, and a discharge branch. Each capacitor bank consists of multiple parallel-connected power capacitors. A corresponding switching unit is provided on the branch of each capacitor bank. The switchable damping branch is a resistor, an RC branch, or an RL branch connected in series with the switching unit to form an energy-dissipating branch. The discharge branch is a branch formed by a switching unit and a resistor connected in series. Each switching unit can be a contactor, a solid-state switch, a hybrid switch, or other switching devices suitable for high-voltage, high-current scenarios. The positive main busbar is connected to an upstream converter or upstream power source via a main circuit switch. The present invention does not limit the specific device types of the switchable damping branch and the switching unit; any device capable of controlled damping, controlled capacity reduction, topology reconfiguration, and fault isolation can be applied to the present invention.

[0026] A total bus current sensor is installed on the positive main busbar to measure the total bus current. Each capacitor bank is equipped with a branch current sensor to measure the branch current. A bus voltage sensor is installed between the positive and negative main busbars to measure the bus voltage. The resonance suppression system includes a signal acquisition module, a frequency band analysis module, a criterion decision module, and an execution module. The resonance suppression system is used to acquire bus voltage, total bus current, and branch current, and to control the switching of each capacitor bank, switchable damping branch, and discharge branch to suppress resonance. In this embodiment, individual capacitors can be arranged in a horizontally stacked structure to form a double-row parallel capacitor array, for example, 14 capacitors per row, for a total of 28 capacitors connected in parallel. The system rated voltage can be 3500V, and the total current can reach 50kA. The above structural parameters are only examples and do not constitute a limitation of the present invention.

[0027] For the resonance suppression system of the above parallel capacitor, a simplified equivalent model can be established using the following formula:

[0028]

[0029]

[0030] in, For complex variables, The system's equivalent impedance, The system's equivalent resistance. The system's equivalent stray inductance, This is the equivalent capacitance of the parallel capacitor array in the current partition access state. The equivalent resonant frequency, This is the equivalent damping ratio. At the mF level... nH level and mΩ level Under the combined effect, the system may form a strong resonant response in the range of 500 to 2000 Hz.

[0031] like Figure 2 The diagram illustrates the entire process of a resonance suppression system, from acquiring bus voltage, total bus current, and branch currents in different zones, through bandpass analysis in the 500–2000 Hz band, extraction of resonant characteristics, calculation of resonant risk coefficients, and comparison of graded thresholds, to sequentially executing normal monitoring, early warning, primary suppression, secondary suppression, fault isolation and shutdown discharge, and finally exiting the suppression state and gradually restoring the affected zones after meeting recovery conditions. This process is described in conjunction with... Figure 2 The resonance suppression process of this invention is described in detail below: The resonance suppression system first synchronously samples the bus voltage, total bus current, and current in each zone to obtain the bus voltage signal. Busbar total current signal and the q Current signal of each zone .in, , This represents the number of capacitor banks. The above signals are processed by bandpass filters ranging from 500 to 2000 Hz to obtain the bus voltage bandpass signal. Busbar total current on signal and the current bandpass signal of each zone .

[0032] In length of Within the calculation time window, the voltage-mode resonance amplitude is calculated based on the bus voltage bandpass signal:

[0033] in, t For the current calculation time, For integration variables, subscript bp This indicates the signal after bandpass filtering in the 500–2000 Hz range; It is used to characterize the degree of oscillation amplification of bus voltage and capacitor terminal voltage in the 500-2000Hz frequency band. The larger the value, the higher the risk of resonance or overvoltage of the bus voltage within the target frequency band.

[0034] Calculate the current-mode resonance amplitude based on the total bus current bandpass signal:

[0035] in, It is used to characterize the resonant current amplification of the entire parallel capacitor bank in the 500-2000Hz frequency band. The larger the value, the greater the risk of current-mode resonance or series resonance in the parallel capacitor bank as a whole.

[0036] Calculate the first based on the current bandpass signal of each partition. q The local oscillation intensity of each partition within the target frequency band, i.e., the partition resonance amplitude. :

[0037] And calculate the average value of the resonance amplitude of each zone. :

[0038] Further calculation of the zone current difference This characterizes the degree of imbalance in the resonant current distribution between different capacitance zones, and the formula is:

[0039] When the q The resonant amplitude of each capacitor zone The average resonance amplitude of the partition is higher than that of other partitions. times, or An increase indicates that the resonant energy is concentrated and amplified within that region or several regions. This relates to the resonant amplitude of all regions. The partition with the largest median value is determined as the resonance concentration partition, denoted as . This serves as a reference for identifying resonance contribution zones.

[0040] To comprehensively reflect the bus voltage oscillation, overall resonant current amplification, and the degree of concentration of local resonance in different zones, the above amplitude indicators are normalized respectively:

[0041]

[0042]

[0043]

[0044] in, , , and These are the reference values ​​for voltage-source resonance amplitude, current-source resonance amplitude, zone resonance amplitude, and zone current difference obtained under normal system conditions. , , , These are normalized indices for voltage-type resonant amplitude, current-type resonant amplitude, zone resonant amplitude, and zone current difference, respectively.

[0045] Resonance amplitude index Calculated using a weighted fusion method:

[0046] in, These are the weighting coefficients for the voltage-source resonant amplitude, current-source resonant amplitude, zone resonant amplitude, and zone current difference, respectively, and they satisfy the following:

[0047] From this, we obtain It is a dimensionless composite resonance amplitude index. The larger the value, the higher the overall resonance risk of the system within the target frequency band of 500–2000 Hz. Among these, the current-mode resonance amplitude is mainly used to assess the risk of low-impedance resonance, series resonance, or current-mode resonance; the voltage-mode resonance amplitude is mainly used to assess bus voltage oscillation and overvoltage risk; and the regional resonance amplitude and regional current differences are mainly used to assess local resonance, regional circulating current amplification, and the location of resonance concentration. Through the above comprehensive calculations, the resonance amplitude index... It can simultaneously reflect overall current amplification, bus voltage oscillation, and zone current imbalance, avoiding misjudgment caused by relying on a single electrical quantity.

[0048] The equivalent damping index can be estimated based on the logarithmic decrease rate of adjacent oscillation peaks. Specifically, for the selected resonant observation bandpass signal, two adjacent in-phase peaks or envelope peaks are extracted, and the logarithmic attenuation rate is calculated. Damping parameters are calculated based on the logarithmic decay rate. :

[0049]

[0050] in, Indicates the first bandpass signal The amplitude of each oscillation peak. If the current risk is mainly triggered by the bus voltage bandpass amplitude, then The signal is taken from the bus voltage bandpass signal; if the current risk is mainly triggered by the current-mode resonant amplitude, then... The signal is taken from the total bus current bandpass signal; if the current risk is mainly triggered by the current bandpass amplitude of a certain zone, then... The signal is taken from the current passband signal of this partition. Logarithmic attenuation rate. This is used to characterize the decay rate of the oscillation amplitude. If adjacent peaks decay rapidly, it indicates that the system is well damped; if adjacent peaks decay slowly or even continue to increase, it indicates that the system is poorly damped and there is a risk of persistent resonance.

[0051] The growth rate index can also be obtained based on the amplitude changes in adjacent sampling periods. Growth rate indicator This is used to characterize the enhancement trend of the resonant amplitude between adjacent sampling windows. Specifically, in the first... k The resonance amplitude index is obtained within each sampling window. The resonance amplitude index is obtained within the previous sampling window. The growth rate indicator is calculated according to the following formula:

[0052] in, To prevent extremely small positive numbers with a denominator of zero. When When the value is greater than zero, it indicates that the resonant amplitude in the target frequency band shows an increasing trend relative to the previous sampling window; when A sustained increase or exceeding a set threshold indicates a risk of continuous resonance amplification within the system. When the resonance amplitude decreases or remains stable, the growth rate indicator is set to zero to avoid misinterpreting transient disturbance decay as continuous resonance.

[0053] Resonance risk coefficient It can be calculated using the following formula:

[0054] in, , , All are weighting coefficients, representing the weights of the resonance amplitude term, growth rate term, and damping insufficiency term in the resonance risk coefficient, respectively. The three are determined based on the system protection sensitivity and engineering commissioning results. The resonant amplitude reference value can be taken as the upper limit of the target frequency bandpass amplitude, the warning threshold, or the reference amplitude obtained by test calibration under normal system conditions, and is used to normalize the resonant amplitude index. The growth rate reference value can be taken as the threshold for judging a significant increase in the resonance amplitude or the growth rate benchmark value obtained through experimental calibration, and is used to normalize the growth rate index. This represents the damping reference value, which can be the lowest damping level allowed when the system is in a stable operating state or the damping threshold obtained through test calibration.

[0055] In the above formula, the resonance amplitude term reflects whether the oscillation intensity within the current target frequency band is too large, the growth rate term reflects whether the resonance is in a state of continuous enhancement, and the damping insufficiency term reflects whether the oscillation is difficult to decay naturally. These three types of indicators work together to calculate the resonance risk coefficient, avoiding misjudgments caused by relying solely on a single voltage or current peak value, thus enabling the distinction between short-term disturbances and continuous resonance.

[0056] when At that time, the system continues to operate normally. To restore the threshold; when When this occurs, the system enters an early warning state, records the resonant frequency, resonant amplitude, and zonal distribution, and can output an alarm signal to the host computer. This is the first-order inhibition threshold; when hour, To reach the fault isolation threshold, the system enters Level 1 suppression mode. First, the switchable damping branch is engaged to increase equivalent damping and reduce oscillation amplitude. After engaging the switchable damping branch, the resonance suppression system enters the Level 1 suppression observation phase. If, during the Level 1 suppression observation phase... continuous Time higher or growth rate indicators continuous Time exceeds the set growth rate threshold If the first-level inhibition is insufficient, then the second-level inhibition action is executed. The value range is 20ms to 200ms, preferably 50ms. Secondary suppression actions include cutting off at least one capacitor bank, reducing the equivalent capacitance, and changing the connection status of parallel branches to move the equivalent resonant point out of the dangerous frequency band. If necessary, control commands to weaken the excitation source can be sent to the upstream converter to reduce current excitation within a specific frequency band. Reducing the equivalent capacitance mainly refers to reducing the number of capacitor banks in operation. Changing the connection status of parallel branches refers to changing the connection status of each capacitor bank branch. Its core is to adjust which capacitor banks participate in parallel operation through the switching units on each capacitor bank branch. For example... Figure 3 As shown, Figure 3 Figure (a) shows an implementation method that involves engaging a switchable damping branch when resonance occurs to improve the system's equivalent damping and reduce the oscillation amplitude; Figure 3 Figure (b) illustrates an implementation that reduces the equivalent capacitance, shifts the resonant point, and lowers the risk of resonance by removing at least one capacitor partition to achieve partition decapacitation and parallel topology reconstruction.

[0057] By following the sequence of "first increasing damping, then reducing capacitance, and finally isolating," the risk of resonance can be controlled while maintaining the system's continuous operation as much as possible. If Greater than or equal to ,or Higher than And the resonant state is maintained continuously for more than If any one of the following exceeds the safety limit: bus voltage, total bus current, or connection point temperature rise, then a fault isolation action will be immediately executed. The safe limit time for the allowable resonance duration ranges from 0.2s to 2s, preferably 0.5s. Fault isolation actions include disconnecting the main circuit, cutting off the resonance contribution zone, and initiating the discharge branch. Disconnecting the main circuit is achieved by disconnecting the main circuit switch. The resonance contribution zone refers to the zone determined by the resonance suppression system during the resonance suppression process based on the amplitude of the band-current in each capacitor zone, the current growth rate, the correspondence with the total bus current, and the temperature rise at the connection point. q A capacitor region is considered a resonance contribution region when it meets any two of the following conditions: 1) No. q The resonant amplitude of the zone current in the 500-2000Hz frequency band The average amplitude of the zone resonance is higher than that of other capacitor zones. times, The value range is 1.2 to 2.0, preferably 1.5; 2) Current growth rate of the qth partition G q Higher than the average current growth rate of other zones times, The value range is 1.2 to 2.0, preferably 1.5. This indicates that the degree of growth in resonant amplification in this capacitor region is higher than that in other regions; 3) The current in the q-th partition and the total bus current satisfy the same frequency correlation condition. Specifically... Calculate the first q Bandpass signal of capacitor partition current Signal connected to the total bus current correlation coefficient :

[0058] when And satisfy At that time, it was determined that there was an abnormal correlation between the capacitor bank section and the total bus current, indicating that the capacitor bank section was the main path through which the resonant current flowed. The correlation coefficient threshold and The value range is 0.7 to 0.95, preferably 0.8; It is a constant and The value range is 1.2 to 2.0, preferably 1.5; 4) The temperature rise at the connection point of the q-th capacitor section or the amplitude of the section's on-state current reaches a preset limit. Specifically, when the temperature rise at the connection point... Not lower than the temperature rise limit , or the q The resonant amplitude of each capacitor zone Not less than the allowable band current amplitude of the zone When the corresponding switching device, fuse, or temperature sensor in that zone outputs a fault status signal, the zone is determined to have reached an abnormal state. The value range is 20℃~40℃, preferably 30℃; The rated ripple current, current-carrying capacity of the connectors, and temperature rise test results for each capacitor section are determined. After the q-th capacitor section is removed, the resonance suppression system recalculates the resonance risk factor. If the risk factor for resonant resonance before removal is... The risk coefficient of resonance after removal is And satisfy:

[0059] This confirms that the capacitor partition contributes to the resonance risk. It is a constant and The value range is 0.2 to 0.5, preferably 0.3.

[0060] During the recovery phase, when the resonance risk coefficient continuous Time below recovery threshold Furthermore, the bus voltage, total bus current, and temperature rise at the connection points of each zone's current all... continuous When the time remains within the allowable range, the resonance suppression system determines that the resonance has been eliminated and enters the exit suppression process. The value range is 0.5s to 10s, with 2s being the preferred value. The value of is in the range of 0.6 to 0.8, preferably 0.7.

[0061] The resonance suppression system exits the suppression state in a preset sequence: after the recovery exit conditions are met, the resonance suppression system first maintains the current capacitor partition connection state. After a certain time, the switchable damping branch is disconnected, and then the disconnected capacitor sections are restored step by step according to a preset sequence. The value range is 0.5s to 5s, preferably 1s.

[0062] To prevent resonance from being triggered again after recovery, zonal recovery should be carried out in a step-by-step manner, with recalculation performed after each step. Specifically, after each removed capacitor section is restored, the resonance suppression system re-acquires the bus voltage, total bus current, and current of each section, and recalculates the data. If in Within a time The recovery threshold was not exceeded again. K 1, and voltage-mode resonant amplitude Current-mode resonant amplitude , zone resonance amplitude and connection point temperature rise If all remain within acceptable limits, then proceed to restore the next capacitor partition to be removed; if Exceeding the recovery threshold again If the condition is not met, the recovery process will stop and the system will re-enter the resonance suppression judgment process. The value range is 0.2s to 2s, preferably 0.5s.

[0063] This invention does not limit the specific algorithmic form of the resonant characteristic quantity. In addition to the methods based on bandpass analysis, logarithmic decrease, and resonance risk coefficient mentioned above, peak spectral tracking, impedance identification, phase difference monitoring, sliding window energy criterion, or combinations thereof can also be used. As long as the identification and graded suppression of resonance risk in the 500-2000Hz frequency band can be achieved, they all fall within the protection scope of this invention.

[0064] Through the above technical solutions, this invention collects DC bus voltage, total current, and zoned branch current; performs bandpass analysis on the 500–2000 Hz frequency band to extract resonant frequency, in-band energy, amplitude growth rate, and equivalent damping index; determines the resonance state based on the resonance risk coefficient; and sequentially executes actions such as early warning, activating switchable damped branches, zoned decapacitation or parallel topology reconstruction, weakening the excitation source, and fault isolation and shutdown discharge when different thresholds are reached; and exits the suppression state according to hysteresis logic after the recovery conditions are met. It can identify and suppress resonance before overcurrent and overvoltage peaks form, shorten the duration of dangerous oscillations, reduce the electrothermal stress on the busbar, capacitor terminals, and connection interfaces, and balance safety, recoverability, and continuous system operation capability.

[0065] Example 2 Embodiment 2 of the present invention provides a resonance suppression system for parallel capacitors, implementing the resonance suppression method described in Embodiment 1, applied to a parallel capacitor topology circuit. The parallel capacitor topology circuit includes at least two capacitor partitions connected in parallel, a switchable damping branch, and a discharge branch. The resonance suppression system includes: The signal acquisition module is used to acquire bus voltage, total bus current, and zone current of at least two capacitor banks; The frequency band analysis module is used to perform bandpass analysis on the acquired signal to obtain various indicators characterizing the resonance state. The criterion decision module is used to construct a resonance risk coefficient based on various indicators and compare it with the graded threshold, and output graded suppression instructions. The execution module is used to perform early warning, resonance suppression, and fault isolation actions in a predetermined sequence when the resonance risk coefficient reaches a preset condition; when the resonance risk coefficient continuously... Time below recovery threshold Furthermore, the bus voltage, total bus current, current in each zone, and temperature rise at connection points are all continuous. When the time remains within the allowable range, the system is determined to meet the recovery exit condition and exits the resonance suppression state.

[0066] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for suppressing resonance in a parallel capacitor, characterized in that, The method for suppressing resonance is applied to a parallel capacitor topology circuit, which includes at least two capacitor banks connected in parallel, a switchable damping branch, and a discharge branch. S1. Collect bus voltage, total bus current, and current of at least two capacitor banks; S2. Perform bandpass analysis on the acquired signal to obtain various indicators characterizing the resonance state; S3. Construct a resonance risk coefficient based on various indicators and compare it with the graded threshold, then output a graded suppression command; when the resonance risk coefficient reaches the preset condition, execute the warning, resonance suppression, and fault isolation actions in a predetermined order; when the resonance risk coefficient continuously reaches the preset condition, execute the warning, resonance suppression, and fault isolation actions in a predetermined order. Time below recovery threshold Furthermore, the bus voltage, total bus current, current in each zone, and temperature rise at connection points are all continuous. When the time remains within the allowable range, the system is determined to meet the recovery exit condition and exits the resonance suppression state.

2. The resonance suppression method for a parallel capacitor according to claim 1, characterized in that, The switchable damping branch is an energy-consuming branch formed by connecting a resistor, RC branch, or RL branch in series with the switching unit.

3. The resonance suppression method for a parallel capacitor according to claim 1, characterized in that, The discharge branch is a branch formed by a switching unit and a resistor connected in series.

4. The resonance suppression method for a parallel capacitor according to claim 1, characterized in that, Each capacitor bank consists of multiple power capacitors connected in parallel, and a corresponding switching unit is set on the branch where each capacitor bank is located.

5. The resonance suppression method for a parallel capacitor according to claim 1, characterized in that, S2 includes: Bandpass analysis was performed on the collected signals in the 500–2000 Hz frequency band to obtain the resonance amplitude index, growth rate index, and damping index, which characterize the resonance state.

6. The resonance suppression method for a parallel capacitor according to claim 5, characterized in that, The damping index is calculated using the logarithmic decrease rate of adjacent oscillation peaks, the bandpass impedance phase offset, the equivalent damping ratio, or a weighted combination thereof.

7. The resonance suppression method for a parallel capacitor according to claim 6, characterized in that, The resonance risk coefficient is calculated as follows: Calculate the resonance amplitude index ,in, These are the weighting coefficients for the voltage-source resonant amplitude, current-source resonant amplitude, zone resonant amplitude, and zone current difference, respectively, and satisfy the following conditions: , , , , These are normalized indices for voltage-mode resonance amplitude, current-mode resonance amplitude, zone resonance amplitude, and zone current difference, respectively. growth rate indicators The value is obtained based on the amplitude change in adjacent sampling periods. Growth rate index within a sampling window in, For the first The resonance amplitude index within each sampling window It is a positive number; Damping index , This represents the logarithmic decrease rate between adjacent oscillation peaks and , Indicates the first bandpass signal The amplitude of each oscillation peak; Resonance risk coefficient ,in, , , All are weighted coefficients. This represents the reference value for the resonance amplitude. This represents a reference value for the growth rate. This indicates the damping reference value.

8. The resonance suppression method for a parallel capacitor according to claim 7, characterized in that, S3 includes: when At that time, the system continues to operate normally. To restore the threshold; when When this occurs, the system enters an early warning state, records the resonant frequency, resonant amplitude, and zonal distribution, and outputs an alarm signal to the host computer. This is the first-order inhibition threshold; when hour, To reach the fault isolation threshold, the system enters Level 1 suppression mode. First, the switchable damping branch is engaged. After engaging the switchable damping branch, the resonance suppression system enters the Level 1 suppression observation phase. If, during the Level 1 suppression observation phase... continuous Time higher or growth rate indicators continuous Time exceeds the set growth rate threshold If the first-level suppression is insufficient, the second-level suppression action is executed. The second-level suppression action includes cutting off at least one capacitor section, reducing the equivalent capacitance, changing the connection status of the parallel branch, and sending a control command to the upstream converter to weaken the excitation source. like Greater than or equal to ,or Higher than And the resonant state is maintained continuously for more than If any one of the following exceeds the safety limit: bus voltage, bus total current, or connection point temperature rise, then a fault isolation action shall be immediately performed. The fault isolation action includes disconnecting the main circuit, cutting off the resonant contribution zone, and starting the discharge branch. when continuous Time below recovery threshold Furthermore, the bus voltage, total bus current, current in each zone, and temperature rise at connection points are all continuous. When the time remains within the allowable range, the resonance suppression system first maintains the current capacitor partition connection state. After a certain time, the switchable damping branch is disconnected, and then the removed capacitor sections are restored step by step in a preset order. After each removed capacitor section is restored, if... Within a time The recovery threshold was not exceeded again. And voltage-mode resonance amplitude Below the allowable bandwidth of the bus voltage Current-mode resonant amplitude Below the allowable bandwidth of the total bus current , zone resonance amplitude Below the zone's allowable band current amplitude And the temperature rise at the connection point Below the temperature rise limit If so, continue to restore the next cut capacitor partition; if Exceeding the recovery threshold again If the condition is not met, the recovery process will stop and the process will re-enter the resonance suppression judgment process.

9. A method for suppressing resonance in a parallel capacitor according to claim 8, characterized in that, The The value range is 20ms to 200ms. The value range is 0.2s to 2s. The value range is 0.5s to 10s. The value range is 0.5s to 5s, the aforementioned The value range is 0.2s to 2s.

10. A resonance suppression system for parallel capacitors, characterized in that, The resonance suppression method according to any one of claims 1-9 is applied to a parallel capacitor topology circuit, wherein the parallel capacitor topology circuit includes at least two capacitor partitions connected in parallel, a switchable damping branch, and a discharge branch, and the resonance suppression system includes: The signal acquisition module is used to acquire bus voltage, total bus current, and zone current of at least two capacitor banks; The frequency band analysis module is used to perform bandpass analysis on the acquired signal to obtain various indicators characterizing the resonance state. The criterion decision module is used to construct a resonance risk coefficient based on various indicators and compare it with the graded threshold, and output graded suppression instructions. The execution module is used to perform early warning, resonance suppression, and fault isolation actions in a predetermined sequence when the resonance risk coefficient reaches a preset condition; when the resonance risk coefficient continuously... Time below recovery threshold Furthermore, the bus voltage, total bus current, current in each zone, and temperature rise at connection points are all continuous. When the time remains within the allowable range, the system is determined to meet the recovery exit condition and exits the resonance suppression state.

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