A direct current ripple adaptive monitoring and protection method based on magnetic hysteresis accumulation

Abstract

The application discloses a DC ripple adaptive monitoring and protection method based on magnetic hysteresis accumulation, relates to the technical field of power electronic system protection, extracts ripple components through inductive coupling elements in series with a DC bus, and realizes passive frequency adaptive compensation by using the magnetic core loss characteristics and compensation resistance, so that the driving energy is matched with the electrolytic capacitor ripple damage characteristics; the irreversible magnetization and remanence characteristics of the rectangular magnetic hysteresis loop magnetic core are used to convert the ripple damage into the non-volatile physical accumulation of magnetic flux, and the accumulated state can be maintained after power-off; when the magnetic flux approaches saturation, the trigger signal is passively generated by using the magnetic permeability sharp drop characteristics, and the switch device is used to cut off the bus power supply. The application can realize frequency adaptive weighting, intermittent working condition continuous accumulation and inverse time limit protection without an auxiliary power supply and digital algorithm, and is suitable for multiple working conditions to realize reliable electrolytic capacitor ripple damage protection of the DC bus.

Description

Technical Field

[0001] This invention belongs to the field of power electronic system protection technology, specifically relating to a DC ripple adaptive monitoring and protection method based on hysteresis accumulation. Background Technology

[0002] In power electronic equipment such as switching power supplies, photovoltaic grid-connected inverters, energy storage converters, and industrial servo drives, DC bus electrolytic capacitors are crucial energy storage and filtering devices, primarily used to stabilize bus voltage and absorb high-frequency switching ripple. During equipment operation, factors such as power device switching, grid harmonic disturbances, and sudden load changes can generate broadband ripple current on the DC bus. This ripple current flowing through the equivalent series resistance (ESR) of the electrolytic capacitor generates heat loss. Long-term heat accumulation can lead to electrolyte evaporation, capacity reduction, and increased ESR, potentially resulting in capacitor bulging, leakage, and breakdown, affecting the normal operation and safety of the equipment.

[0003] Currently, the main methods for monitoring and protecting against ripple damage to electrolytic capacitors on DC buses include two types: digital monitoring and protection, and analog threshold protection. One type is the digital I²t accumulation protection method based on ADC sampling and microcontroller. This method samples the bus ripple current and performs analog-to-digital conversion, then the processor performs digital integration to accumulate ripple energy. Protection is triggered when the accumulated amount reaches a set threshold. This method relies on an auxiliary power supply and a processor; the integration data is difficult to retain after power failure, making continuous accumulation of damage impossible under intermittent equipment operation. Furthermore, it is prone to sampling deviations and computational anomalies under conditions of strong electromagnetic interference and high temperatures, limiting its adaptability to the working environment.

[0004] Another type is the threshold delay protection method that uses an analog comparator in conjunction with an RC integrator circuit. The comparator determines whether the ripple amplitude exceeds the limit, and if it does, the RC integrator circuit performs voltage integration to achieve a delayed trigger. In this type of implementation, the integrating capacitor's charge is easily discharged after power failure, making it difficult to maintain its accumulated state; the same integration weight is used for ripple of different frequencies, resulting in a low frequency matching degree with the ESR loss of the electrolytic capacitor; a fixed amplitude threshold needs to be set, leading to insufficient protection response under long-term low-amplitude ripple conditions, and prone to false triggering under normal ripple conditions.

[0005] Currently, most related technical solutions in this field focus on the electric field signal processing route, which usually uses electronic circuits or digital algorithms to complete the sampling, calculation and accumulation of ripple signals. There is little research on the application of the physical properties of magnetic materials in damage accumulation. When solving the problem of maintaining the accumulated state after power failure, existing solutions mostly use backup power supplies or non-volatile memory. Passive accumulation memory methods based on the remanent magnetization characteristics of rectangular hysteresis loop materials are rarely used. When realizing frequency-weighted damage assessment, related solutions generally use active filters or digital FFT operations. The technical route of passive frequency adaptive compensation based on the inherent loss characteristics of magnetic core has not been fully studied and widely applied.

[0006] In summary, existing technical solutions struggle to simultaneously achieve passive operation, adaptive weighted ripple damage frequency, retention of accumulated values ​​under power-down conditions, and inverse-time protection characteristics, thus limiting their application in the long-term reliable protection of DC bus electrolytic capacitors in industrial settings. Therefore, there is an urgent need in this field for a DC ripple monitoring and protection method that breaks through conventional technical approaches and leverages the physical properties of magnetic materials to achieve end-to-end passive adaptive protection. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a DC ripple adaptive monitoring and protection method based on hysteresis accumulation for monitoring and protecting DC bus electrolytic capacitors from ripple damage, comprising the following steps: S1: The primary winding of the inductive coupling element is connected in series with the DC bus, and the ripple component in the bus current is extracted through the secondary winding, which is magnetically coupled to the primary winding. The inductive coupling element uses the physical loss characteristics of its own magnetic core to perform passive frequency compensation on the extracted ripple component and outputs drive pulse energy. The characteristic of the drive pulse energy of the ripple component at different frequencies changing with frequency is matched with the characteristic of the equivalent series resistance loss power of the electrolytic capacitor changing with the ripple frequency, and the fitting degree is not less than 95% across the entire frequency band. S2: The driving pulse energy is applied to the excitation winding that is magnetically coupled to the accumulating magnetic core. The excitation winding, the rectifier element and the secondary winding of the inductive coupling element are connected in series to form an excitation circuit, so that the driving pulse applied to the excitation winding is unipolar. The excitation winding generates a unipolar magnetic field strength pulse in the accumulating magnetic core with rectangular hysteresis loop characteristics, driving the magnetic flux of the accumulating magnetic core to generate an irreversible net magnetic flux increment from the current remanent state to the saturation magnetic flux direction, and maintaining the accumulated magnetic flux state by relying on the remanence after the pulse disappears. S3: The magnetic flux state is monitored by the detection winding magnetically coupled to the accumulated magnetic core. When the accumulated magnetic flux reaches the preset magnetic saturation threshold, the characteristic of the accumulated magnetic core's permeability dropping sharply, which leads to an increase in the excitation current change rate, is used to generate a voltage spike in the detection winding that is 5 times or more higher than the induced voltage amplitude when the accumulated magnetic core has not reached the magnetic saturation threshold, as a trigger signal. S4: In response to the trigger signal, drive the switching device to cut off the DC bus power supply.

[0008] Preferably, the passive frequency compensation step in step S1 includes: The magnetic core material whose loss tangent increases with increasing frequency is selected as the magnetic core of the inductive coupling element. This makes the magnetic core loss generated by the higher frequency ripple component in the magnetic core greater, and the corresponding drive pulse energy output by the secondary winding attenuation greater. This matches the characteristic that the equivalent series resistance loss of the electrolytic capacitor decreases with increasing ripple frequency. A compensation resistor is connected in parallel at the output terminal of the secondary winding of the inductive coupling element. By adjusting the resistance value of the compensation resistor, the characteristic of the driving pulse energy output by the inductive coupling element changing with the ripple frequency under the same ripple current amplitude is matched with the characteristic of the power loss of the equivalent series resistance of the electrolytic capacitor changing with the ripple frequency.

[0009] Preferably, the resistance value of the compensation resistor is selected to satisfy the following: within the ripple frequency variation range of the electrolytic capacitor, the time integral value of the driving pulse energy and the time integral value of the power loss of the equivalent series resistance of the electrolytic capacitor maintain a fixed preset ratio.

[0010] Preferably, the irreversible net magnetic flux increment in step S2 is achieved in the following way: A high remanence ratio rectangular hysteresis loop soft magnetic material is selected as the accumulation core. When the magnetic field strength generated by the driving pulse energy exceeds the coercivity of the accumulation core, the domain walls inside the core undergo irreversible displacement. After the magnetic field is removed, the core stabilizes at a new remanence point, generating a net magnetic flux increment corresponding to a single ripple event. Under multiple ripple events, the cumulative magnetic flux is the sum of the net magnetic flux increments of each event. The cumulative magnetic flux is positively correlated with the total cumulative damage of the electrolytic capacitor. The cumulative magnetic flux is maintained by the residual magnetism after the DC bus is de-energized, and the magnetic flux retention rate is not less than 99% after the DC bus is de-energized for at least 72 hours.

[0011] Preferably, the cumulative damage D of the electrolytic capacitor satisfies , Where n is the total number of ripple events within the statistical time period; I ripple,i Δt represents the effective value of the ripple current corresponding to the i-th ripple event. 1,iis the duration of the i-th ripple event; k1 is a constant related to the equivalent series resistance, thermal resistance, and aging characteristics of the electrolytic capacitor; The magnetic flux accumulation Φ satisfies , Where n is the total number of ripple events within the statistical time period; H exceed,i For the i-th ripple event, exceeding the core coercivity H c The magnetic field strength component, i.e. ; H i H represents the instantaneous magnetic field strength generated by the excitation winding in the accumulating core during the i-th ripple event; c The coercivity of the magnetic core at the operating temperature; Δt 2,i For the i-th ripple event, H exceed,i The total duration of the continuous time period >0; k2 is a constant related to the properties of the magnetic core material and the magnetic circuit parameters.

[0012] When the accumulated magnetic flux Φ reaches the preset magnetic saturation threshold Φ th When the cumulative damage D of the electrolytic capacitor reaches the preset protection limit value D, th This ensures that the protection trigger time corresponds to the actual degree of damage to the electrolytic capacitor.

[0013] Preferably, in step S2, the excitation windings of multiple groups of cumulative magnetic cores with different coercivity parameters are connected in parallel to the same excitation circuit, and each group of cumulative magnetic cores responds to ripple events with different amplitude ranges. In step S3, the piecewise fitting of the electrolytic capacitor damage curve is achieved by monitoring the saturation timing and combination state of each group of cumulative magnetic cores.

[0014] Preferably, a negative temperature coefficient thermistor is connected in series in the excitation circuit of step S2. By utilizing the characteristic that the resistance of the negative temperature coefficient thermistor decreases with increasing temperature, the magnitude of the excitation current is automatically adjusted so that the net magnetic flux increment generated by a single ripple event increases with increasing temperature, thereby adaptively matching the magnetic flux accumulation rate with the temperature-dependent damage acceleration characteristics of the electrolytic capacitor.

[0015] Preferably, in step S3, the amplitude of the voltage spike induced by the detection winding is not lower than the gate turn-on threshold voltage of the switching device; when the accumulated magnetic core has not reached the magnetic saturation near threshold, the amplitude of the induced voltage generated by the normal ripple event in the detection winding is insufficient to trigger the switching device to turn on.

[0016] Preferably, the method further includes step S5: after disconnecting the DC bus power supply and completing the fault investigation, a reverse current pulse is applied to the excitation winding of the accumulated magnetic core to restore the magnetic flux of the accumulated magnetic core from the state of reaching the magnetic saturation threshold to the initial residual magnetism state.

[0017] Preferably, when the magnetic field strength generated by the driving pulse energy does not exceed the coercivity of the accumulating magnetic core, the accumulating magnetic core operates in the reversible magnetization range and does not generate net magnetic flux accumulation.

[0018] The beneficial effects of this invention are: 1. By combining the inherent loss characteristics of the magnetic core of the inductive coupling element with the compensation resistor, passive frequency adaptive compensation is achieved. Without active filtering or digital frequency domain calculation, the ripple drive energy characteristics can be accurately matched with the ESR loss frequency characteristics of the electrolytic capacitor. This solves the problem of mismatch between frequency weighting and actual damage in traditional schemes from a physical perspective, and improves the matching accuracy of ripple damage monitoring.

[0019] 2. This invention utilizes the irreversible hysteresis magnetization and remanence characteristics of a rectangular hysteresis loop core to transform the accumulation of ripple thermal damage into the physical accumulation of magnetic flux. It can achieve non-volatile retention of the accumulated state after power failure without the need for a backup power supply and non-volatile memory. It can complete the continuous accumulation of damage under intermittent start-stop conditions of the equipment, and overcomes the inherent defect of loss of accumulation when power is off in traditional solutions.

[0020] 3. This invention relies on the physical characteristics of the sharp drop in permeability in the near-saturation region of the accumulated magnetic core and the natural threshold of coercivity to passively generate a protection trigger signal, thereby achieving the inverse-time protection characteristics of fast triggering for large ripples and slow accumulation for small ripples. It does not require active devices such as processors and comparators, and can still stably perform protection actions under strong electromagnetic interference and high-temperature conditions, thus improving system reliability. Attached Figure Description

[0021] Figure 1 This is a flowchart illustrating the steps of the DC ripple adaptive monitoring and protection method based on hysteresis accumulation as described in an embodiment of the present invention. Figure 2 This is a comparison curve of the passive frequency adaptive compensation characteristics described in the embodiments of the present invention; Figure 3 This is a graph showing the irreversible hysteresis accumulation and triggering characteristics as described in an embodiment of the present invention. Detailed Implementation

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described content is only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0023] The features and effects of the present invention will be further described in detail below with reference to embodiments.

[0024] In one feasible implementation, a DC ripple adaptive monitoring and protection method based on hysteresis accumulation is provided for ripple damage monitoring and protection of DC bus electrolytic capacitors, such as... Figure 1 As shown, it includes the following steps: Step S1: The primary winding of the inductive coupling element is connected in series with the DC bus, and the ripple component in the bus current is extracted through the secondary winding that is magnetically coupled to the primary winding. The inductive coupling element uses the physical loss characteristics of its own magnetic core to perform passive frequency compensation on the extracted ripple component and outputs drive pulse energy. The characteristic of the drive pulse energy of the ripple component at different frequencies changing with frequency is matched with the characteristic of the equivalent series resistance loss power of the electrolytic capacitor changing with the ripple frequency, and the fitting degree is not less than 95% across the entire frequency band. Step S2: The driving pulse energy is applied to the excitation winding that is magnetically coupled to the accumulating magnetic core. The excitation winding, the rectifier element, and the secondary winding of the inductive coupling element are connected in series to form an excitation circuit, so that the driving pulse applied to the excitation winding is unipolar. The excitation winding generates a unipolar magnetic field strength pulse in the accumulating magnetic core with rectangular hysteresis loop characteristics, driving the magnetic flux of the accumulating magnetic core to generate an irreversible net magnetic flux increment from the current remanent state to the saturation magnetic flux direction, and maintaining the accumulated magnetic flux state by relying on the remanence after the pulse disappears. Step S3: Monitor the magnetic flux state through the detection winding magnetically coupled to the accumulated magnetic core. When the accumulated magnetic flux reaches the preset magnetic saturation threshold, take advantage of the characteristic that the magnetic permeability of the accumulated magnetic core drops sharply, causing the excitation current change rate to increase, and generate a voltage spike in the detection winding that is 5 times or more higher than the induced voltage amplitude when the accumulated magnetic core has not reached the magnetic saturation threshold as a trigger signal. Step S4: In response to the trigger signal, drive the switching device to cut off the DC bus power supply.

[0025] In this embodiment, the full-band fitting degree refers to the degree of matching between the characteristic curve of the driving pulse energy changing with frequency and the characteristic curve of the equivalent series resistance loss power of the electrolytic capacitor changing with frequency within the 1kHz~100kHz ripple frequency range of the electrolytic capacitor's operation. The maximum relative deviation of no more than ±5% is used as the criterion for a fitting degree of ≥95%.

[0026] Inductive coupling elements refer to current-type passive coupling devices based on the principle of electromagnetic induction. Their core function is to isolate the DC component in the DC bus and only couple and extract the AC ripple component. Their working principle follows Faraday's law of electromagnetic induction, and the induced electromotive force of the secondary winding satisfies the formula: , Where e2 is the induced electromotive force of the secondary winding of the inductive coupling element, in volts (V), and N2 is the number of turns in the secondary winding. The rate of change of magnetic flux in the magnetic core is expressed in Weber per second (Wb / s).

[0027] A constant DC current in a DC bus can only produce a constant magnetic flux in the magnetic core. =0, therefore there is no induced electromotive force output in the secondary winding. Only the changing ripple current can generate alternating magnetic flux, which induces an AC voltage corresponding to the ripple in the secondary winding, thus achieving natural isolation between the DC component and the ripple component.

[0028] The irreversible net flux increment refers to the net change in magnetic flux that can be stably maintained after the magnetic domain walls undergo irreversible displacement under a single driving pulse. This increment only occurs when the magnetic field strength generated by the driving pulse exceeds the coercivity of the magnetic core. It will not return to zero after the pulse is removed and is the core carrier of the physical accumulation of ripple damage.

[0029] The rectangular hysteresis loop characteristic refers to the hysteresis loop of the magnetic core material being approximately rectangular. The core quantitative indicator is the remanence ratio (remanent magnetic flux density B). r / Saturation magnetic flux density B s ≥0.8, coercivity H c Dispersion ≤ ±5%, where B r The residual magnetic flux density of the accumulated magnetic core, measured in Tesla (T); B s The saturation magnetic flux density of the accumulated magnetic core, measured in Tesla (T); H c The coercivity of the accumulated magnetic core is measured in amperes per meter (A / m). This characteristic ensures that the core can stably maintain its remanence after the external magnetic field is removed, and the net flux increment of a single magnetization can be stably reproduced.

[0030] The magnetic saturation threshold refers to a pre-set critical value for magnetic flux, which is taken as the cumulative core saturation magnetic flux Φ. s 85%~95%, Φ s The unit is Weber (Wb). Within this range, the differential permeability of the magnetic core will drop sharply as the magnetic flux increases, with a decrease of ≥90%. This can stably generate a recognizable trigger signal, while reserving a margin of 5%~15% to avoid the magnetic core failing to generate a sufficient rate of change of magnetic flux after it has fully entered deep saturation.

[0031] Unipolar magnetic field strength pulse: refers to a magnetic field pulse with a fixed direction that only produces positive magnetization. In this embodiment, it is achieved by connecting a rectifier diode in series in the excitation circuit to ensure that the AC ripple voltage induced by the secondary winding can only output a positive half-wave pulse, avoiding the demagnetizing effect of the reverse pulse and canceling the accumulated magnetic flux.

[0032] In this embodiment, the inductive coupling element can be implemented using various magnetic coupling structures, preferably a current transformer structure. In one feasible implementation, the element specifically adopts a toroidal magnetic core through-hole current transformer structure, with the primary winding connected in series with a single turn via the DC bus main circuit; the secondary winding is wound uniformly in the same direction, and the number of turns N2 satisfies the formula: , This formula is applicable to linear coupling scenarios with sinusoidal ripple components from 1kHz to 100kHz, where 4.44 is the effective value to peak value conversion factor of the sinusoidal wave. For non-sinusoidal pulse ripple, it can be modified to a value in the range of 4.0 to 4.5. f The minimum ripple operating frequency adapted to the target is set to half the nominal switching frequency of the DC bus switching device to ensure attenuation-free coupling across the entire operating frequency range; U out The target secondary-side output voltage amplitude must meet the following requirements: at the lowest frequency rated ripple current, the secondary-side output peak voltage ≥ 1.5 × the excitation threshold voltage corresponding to the cumulative core coercivity, ensuring the generation of effective excitation pulses; where Uout is the target secondary-side output voltage amplitude in volts (V), f is the lower limit of the ripple operating frequency in hertz (Hz), Bcore is the core operating magnetic flux density in tesla (T), and Acore is the effective cross-sectional area of ​​the core in square meters (m²). 2 The complete excitation circuit topology is connected in the following order: one end of the secondary winding of the inductive coupling element, the anode of the rectifier element, the cathode of the rectifier element, the input terminal of the excitation winding, the output terminal of the excitation winding, and the other end of the secondary winding, forming a closed series circuit. The rectifier element is a device with unidirectional conductivity, used to rectify the AC pulses output from the secondary winding into unipolar drive pulses, allowing only the forward half-ripple current to pass through, thus forming a unipolar excitation circuit. The rectifier element is preferably a rectifier diode; in this embodiment, a fast recovery diode with a reverse recovery time ≤ 50ns is selected. Its anode is connected to one end of the secondary winding, and its cathode is connected to the input terminal of the excitation winding. The forward current matches the rated current of the excitation circuit, and the reverse withstand voltage is ≥ 50V.

[0033] The accumulator core is made of a soft magnetic material with rectangular hysteresis loop characteristics, such as permalloy, amorphous nanocrystalline alloy, or MnZn power ferrite. It requires a remanence ratio Br / Bs ≥ 0.8 and a coercivity Hc dispersion ≤ ±5%. In this embodiment, the accumulator core is specifically a 1J85 permalloy toroidal core, with a remanence ratio Br / Bs ≥ 0.90, coercivity Hc ≤ 8 A / m, saturation flux density Bs = 0.82 T, effective magnetic path length Le = 6.0 cm, and effective cross-sectional area Ae = 0.5 cm². 2 The excitation winding and the detection winding are wound in the same direction on the same magnetic core, and the number of turns Nex of the excitation winding satisfies the formula: , Among them, I ex The rated excitation current of the excitation circuit is taken as the peak value of the secondary rectified output current corresponding to 1.2 times the rated ripple current of the DC bus, which can be obtained by formula: Calculations show that Among them I ripple The rated ripple current of the DC bus is the effective value, N1 is the number of turns in the primary winding (N1=1 when it is a single-turn through-core), N2 is the number of turns in the secondary winding, and η is the coupling efficiency, which takes a value of 0.85~0.95 and can be directly used to calculate the number of turns; where H c L represents the coercivity of the magnetic core, measured in amperes per meter (A / m). e I represents the effective magnetic circuit length of the magnetic core, expressed in meters (m). ex The rated excitation current of the excitation circuit is expressed in amperes (A). The number of turns of the detection winding is 0.3 to 0.8 times that of the excitation winding to ensure that the induced voltage is below the switching device's turn-on threshold when not saturated, and can reliably drive the switching device when saturation is approaching.

[0034] The switching device in the protection execution circuit is a semiconductor switch with sufficient voltage and current ratings, capable of reliably cutting off the DC bus power supply according to the trigger signal, such as a power MOSFET, IGBT, or thyristor. In this embodiment, the switching device is specifically selected as an N-channel power MOSFET with a gate turn-on threshold of 2V~4V. A current-limiting resistor is connected in series between the gate and the detection winding, and the resistance value meets the following requirements. , Where R limit This is the resistance value of the gate current-limiting resistor, in ohms (Ω), V. det(max) To detect the maximum output voltage of the winding, the unit is volts (V), I g(max) This is the maximum allowable gate current of the MOSFET, in amperes (A). The drain of the MOSFET is connected in series with the DC contactor coil. The power supply circuit of the contactor coil is connected in series between the positive and negative terminals of the DC bus. This power supply circuit consists of the drain-source path of the contactor coil and the MOSFET connected in series. The rated operating voltage of the contactor coil matches the DC bus voltage. The main contacts of the contactor are connected in series to the main circuit of the DC bus. Under normal conditions, the MOSFET is cut off, the coil is not energized, and the main contacts remain closed. When the induced voltage of the detection winding exceeds the gate turn-on threshold of the MOSFET, the MOSFET turns on, the coil is energized and closes, the main contacts open, and the power supply to the bus is cut off. To avoid false accumulation caused by external magnetic field interference, the accumulation core is fully magnetically shielded with a permalloy shield. The shield has a permeability ≥10000, which can suppress interference from external power frequency magnetic fields and switching magnetic fields. At the same time, a bidirectional transient voltage suppressor diode (TVS) is connected in series in the excitation circuit. The clamping voltage is ≥1.5 × the maximum rated excitation voltage to suppress false excitation pulses caused by bus surges. The TVS is preferably of a power rating of 1.5kW or higher.

[0035] In this embodiment, the method is implemented as follows: When step S1 is executed, the DC component of the DC bus generates a constant magnetic field in the core, and there is no induced output on the secondary side; the alternating magnetic field generated by the ripple current is coupled to the secondary side, and after rectification, a positive drive pulse is output. The core, through its own frequency-dependent loss characteristics, makes the output drive pulse energy positively correlated with the damage of a single ripple to the electrolytic capacitor.

[0036] When step S2 is executed, the driving pulse generates a unipolar magnetic field strength pulse in the excitation winding, and the magnetic field strength H satisfies ; Where H is the magnetic field strength generated by the excitation winding in the accumulating core, and the unit is amperes per meter (A / m). When H exceeds the coercivity of the magnetic core, the magnetic flux undergoes an irreversible net increase. After the pulse disappears, the magnetic core relies on residual magnetism to maintain the accumulation state. Under multiple ripple events, the magnetic flux gradually accumulates irreversibly.

[0037] When step S3 is executed, if the magnetic core has not reached the near-saturation threshold, the induced voltage in the detection winding is lower than the turn-on threshold of the MOSFET. When the accumulated magnetic flux reaches the preset near-saturation threshold, the differential permeability of the accumulated magnetic core drops sharply, causing the equivalent inductance of the excitation circuit to decrease sharply, which in turn causes an instantaneous increase in the excitation current change rate di / dt. Utilizing this physical characteristic, the increased current change rate induces a voltage spike in the detection winding with an amplitude exceeding the turn-on threshold of the MOSFET, which serves as the trigger signal.

[0038] When step S4 is executed, the trigger signal drives the MOS transistor to conduct, the contactor coil is energized, and the main contacts open to cut off the DC bus power supply.

[0039] This embodiment constructs a DC ripple monitoring and protection closed loop based entirely on physical characteristics. Through electromagnetic induction ripple extraction, irreversible accumulation of rectangular hysteresis loop, and passive triggering of permeability drop, the entire physical link eliminates the dependence on auxiliary power supply and digital processing chip. All signal processing and state accumulation are completed through the electromagnetic characteristics of the magnetic core, without the participation of active devices, achieving highly reliable monitoring and protection with long-term maintenance of accumulated state and microsecond-level instantaneous response after power failure.

[0040] In one feasible implementation, the passive frequency compensation step in step S1 includes: The magnetic core material whose loss tangent increases with increasing frequency is selected as the magnetic core of the inductive coupling element. This makes the magnetic core loss generated by the higher frequency ripple component in the magnetic core greater, and the corresponding drive pulse energy output by the secondary winding attenuation greater. This matches the characteristic that the equivalent series resistance loss of the electrolytic capacitor decreases with increasing ripple frequency. A compensation resistor is connected in parallel at the output terminal of the secondary winding of the inductive coupling element. By adjusting the resistance value of the compensation resistor, the characteristic of the driving pulse energy output by the inductive coupling element changing with the ripple frequency under the same ripple current amplitude is matched with the characteristic of the power loss of the equivalent series resistance of the electrolytic capacitor changing with the ripple frequency.

[0041] The value of the compensation resistor is selected to satisfy the following condition: within the range of ripple frequency variation of the electrolytic capacitor, the time integral value of the driving pulse energy and the time integral value of the power loss of the equivalent series resistance of the electrolytic capacitor maintain a fixed preset ratio.

[0042] In this embodiment, the core loss characteristics are selected by using the core loss tangent that satisfies tanδ( f )=k f × f α , where tanδ( f () represents the corresponding frequency f The loss tangent of the lower magnetic core, k f Here, α is the loss coefficient, and α is the frequency exponent, ranging from 1.2 to 1.8. f The ripple frequency is measured in Hertz (Hz). It increases monotonically with increasing frequency in the operating frequency range of 1kHz to 100kHz, without any resonant inflection point.

[0043] The energy of a single drive pulse is positively correlated with the square of the amplitude of the secondary output pulse voltage and negatively correlated with the total equivalent resistance of the excitation circuit. R total The total equivalent resistance of the excitation circuit includes the internal resistance of the secondary winding of the inductive coupling element, the forward conduction resistance of the rectifier diode, the DC resistance of the excitation winding, and the parallel equivalent resistance of the compensation resistor.

[0044] It should be clarified that the passive frequency compensation is intended to adjust the relative weights, not to cut off the high-frequency response. The resistance value of the compensation resistor must be selected to ensure that, at the highest operating frequency, the magnetic field strength generated by the driving pulse energy is still greater than the coercivity of the accumulating magnetic core, thereby ensuring effective monitoring coverage across the entire frequency band. The accumulation rate is only moderately reduced in the high-frequency band to match the actual thermal damage model of the electrolytic capacitor.

[0045] In this embodiment, the magnetic core of the inductive coupling element can be an iron-silicon-aluminum magnetic core, such as KS106-125A, with a relative permeability μr=125, saturation magnetic flux density Bs=1.0T, and effective cross-sectional area Acore=0.654cm². 2 The operating magnetic flux density is set to 20%~30% of the saturation magnetic flux density to ensure operation within the linear range and avoid coupling characteristic distortion caused by magnetic saturation. Other core materials with loss tangents that increase with frequency can also be used. The specific steps for designing and fitting the compensation resistor include: The first step is to obtain the ESR frequency characteristics within the operating frequency range of 1kHz to 100kHz from the target electrolytic capacitor's datasheet, and establish a baseline P for the electrolytic capacitor's loss. loss ( f )=I² ripple ×ESR( f ), where Pl oss ( f () represents the corresponding frequency f The ripple loss power of the lower electrolytic capacitor, in watts (W), I ripple For fixed ripple current amplitude, the unit is ampere (A), ESR ( f () represents the corresponding frequency f The equivalent series resistance of the lower electrolytic capacitor, in ohms (Ω).

[0046] The second step is to test the secondary unloaded output voltage U of the inductive coupling element at different frequencies under a fixed ripple current. oc ( f ), thus obtaining the no-load output characteristic curve. Where U oc ( f () represents the corresponding frequency f The no-load peak output voltage of the secondary winding of the inductive coupling element is given below, in volts (V).

[0047] The third step is to establish a load-carrying output model and connect a parallel compensation resistor R. par Then, the voltage U output from the secondary side to the excitation circuit out ( f )satisfy: , Among them, R parR is the resistance value of the compensation resistor connected in parallel at the output terminal of the secondary winding of the inductive coupling element, expressed in ohms (Ω). load R is the equivalent load resistance of the excitation circuit, which is the sum of the forward conduction resistance of the rectifier diode and the DC resistance of the excitation winding, and its unit is ohms (Ω); s ( f () represents the corresponding frequency f The high-frequency equivalent internal resistance of the lower secondary winding, in ohms (Ω). The equivalent resistance of the compensation resistor and the load resistor in parallel is expressed in ohms (Ω).

[0048] The fourth step is to operate within the range of 1kHz to 100kHz. (C is a fixed preset proportional constant) as the target, Iterative calculation to determine R par The optimal resistance value; the method for determining the fixed preset proportional constant C is as follows: taking a frequency of 1kHz as a reference, under the condition of rated ripple current, take C=U². out (1kHz)×1kHz / P loss (1kHz), where U out (1kHz) is the secondary output voltage under the rated ripple current at 1kHz, P loss (1kHz) represents the ripple loss power of the electrolytic capacitor at the corresponding frequency; the convergence condition for the iterative calculation is: within the full frequency range of 1kHz to 100kHz, (U 2 out ( f )× f ) / P loss ( f The deviation from the reference C is ≤ ±5%, ensuring a full-band fit of ≥ 95%.

[0049] After the compensation resistor is determined, the frequency characteristic fitting degree needs to be verified to be ≥95%; if the attenuation in the high frequency band is insufficient, the resistance value should be reduced, and if the output in the low frequency band is insufficient, the resistance value should be increased, until the fitting requirements are met.

[0050] The passive frequency adaptive compensation characteristic implemented in this embodiment is as follows: Figure 2 As shown.

[0051] Traditional ripple monitoring schemes are generally based on equal-weighted integral theory models, and their ideal accumulation characteristics are as follows: Figure 2 As shown, the contribution of ripple current at different frequencies to the damage of electrolytic capacitors is considered to be exactly the same. However, due to factors such as sampling bandwidth limitations, component temperature drift, and leakage of analog integrators, the actual accumulation rate of existing technologies will have an uncontrollable random deviation within ±15% around this baseline, and these deviations are completely unrelated to the actual damage characteristics of electrolytic capacitors.

[0052] This invention actively controls the variation of the accumulation rate with frequency by leveraging the inherent loss characteristics of the magnetic core and the synergistic effect of the parallel compensation resistor. This ensures that the final accumulation rate curve closely matches the actual ripple damage power curve of the electrolytic capacitor, achieving a fitting accuracy of over 95% across the entire frequency band, with completely controllable deviations. This achieves frequency-adaptive damage weighting without any active filtering or digital algorithms, fundamentally solving the problem of mismatch between the accumulation weight and actual damage in traditional solutions.

[0053] In this embodiment, under completely passive conditions, the cumulative contribution of ripple at different frequencies is precisely matched with the actual thermal damage contribution of the electrolytic capacitor through the synergistic effect of the inherent frequency-related loss of the magnetic core of the inductive coupling element and the parallel compensation resistor. Without the need for active filtering, analog-to-digital conversion or algorithm calculation, pure hardware passively achieves damage weighted adaptive adjustment across the entire frequency band from 1kHz to 100kHz, with a full-band fitting degree of ≥95%, effectively eliminating systematic monitoring errors caused by weight mismatch.

[0054] In one feasible implementation, the irreversible net flux increment in step S2 is achieved in the following manner: A high remanence ratio rectangular hysteresis loop soft magnetic material is selected as the accumulation core. When the magnetic field strength generated by the driving pulse energy exceeds the coercivity of the accumulation core, the domain walls inside the core undergo irreversible displacement. After the magnetic field is removed, the core stabilizes at a new remanence point, generating a net magnetic flux increment corresponding to a single ripple event. Under multiple ripple events, the cumulative magnetic flux is the sum of the net magnetic flux increments of each event. The cumulative magnetic flux is positively correlated with the total cumulative damage of the electrolytic capacitor. The cumulative magnetic flux is maintained by the residual magnetism after the DC bus is de-energized, and the magnetic flux retention rate is not less than 99% after the DC bus is de-energized for at least 72 hours.

[0055] When the magnetic field strength generated by the driving pulse energy does not exceed the coercivity of the accumulating magnetic core, the accumulating magnetic core operates in the reversible magnetization range and does not generate net magnetic flux accumulation.

[0056] The cumulative damage D of the electrolytic capacitor satisfies , Where n is the total number of ripple events within the statistical time period; I ripple,i Δt represents the effective value of the ripple current corresponding to the i-th ripple event. 1,i is the duration of the i-th ripple event; k1 is a constant related to the equivalent series resistance, thermal resistance, and aging characteristics of the electrolytic capacitor; The magnetic flux accumulation Φ satisfies , Where n is the total number of ripple events within the statistical time period; H exceed,i For the i-th ripple event, exceeding the core coercivity Hc The magnetic field strength component, i.e. ; H i H represents the instantaneous magnetic field strength generated by the excitation winding in the accumulating core during the i-th ripple event; c The coercivity of the magnetic core at the operating temperature; Δt 2,i For the i-th ripple event, H exceed,i The total duration of the continuous time period >0; k2 is a constant related to the properties of the magnetic core material and the magnetic circuit parameters.

[0057] When the accumulated magnetic flux Φ reaches the preset magnetic saturation threshold Φ th When the cumulative damage D of the electrolytic capacitor reaches the preset protection limit value D, th This ensures that the protection trigger time corresponds to the actual degree of damage to the electrolytic capacitor.

[0058] In this embodiment, the reversible magnetization range refers to the period when the applied magnetic field strength is lower than the coercivity, and the magnetic flux completely returns to its initial state after the magnetic field is removed, with no net magnetic flux accumulation; the coercivity selection must meet the maximum magnetic field strength H generated by the normal background ripple. bg <0.8×H c Automatically filters out harmless background ripples.

[0059] Net flux increment refers to the net flux increment corresponding to a single pulse. H exceed =H−H c (Only when H>H) c (Effective at the time) to ensure that the amount of damage caused by a single ripple corresponds linearly to the increase in magnetic flux.

[0060] In this embodiment, the accumulation core is made of a rectangular hysteresis loop soft magnetic material with a remanence ratio ≥0.8, such as MnZn power ferrite, permalloy, or amorphous nanocrystalline alloy; the coercivity is matched to the normal background ripple level of the DC bus to avoid false accumulation.

[0061] As mentioned earlier, the linear mapping relationship between the excitation current and the bus ripple current ensures that the ripple amplitude corresponds linearly to the magnetic field strength generated by the excitation winding, providing a basis for the accurate matching of ripple damage and magnetic flux increment.

[0062] The damage-flux matching method is as follows: The first step is to determine the protection limit value D based on the rated ripple current and rated life of the electrolytic capacitor. th A safety margin is reserved for 60% to 80% of the rated life damage.

[0063] The second step is to set a preset magnetic saturation proximity threshold Φ. th It is 85%~95% of the saturation flux of the magnetic core, that is , Where Φ th The preset magnetic saturation threshold is expressed in Weber (Wb). 0.85~0.95 is the flux ratio coefficient, representing the effective range where the magnetic core approaches saturation and the differential permeability drops sharply. The lower limit of 0.85 is used for low coercivity cores, and the upper limit of 0.95 is used for high coercivity cores. The value can be selected within this range based on the core's rectangularity characteristics. B s The cumulative saturation magnetic flux density of the magnetic core, measured in Tesla (T); A e The cumulative effective cross-sectional area of ​​the magnetic core is expressed in square meters (m²). 2 ).

[0064] The third step is to adjust the number of turns in the excitation winding and the turns ratio of the inductive coupling element to match the proportional constants k1 and k2, thereby satisfying the requirements of the above steps. , Wherein, Φ0 is the magnetic flux corresponding to the initial remanence state of the magnetic core. The initial remanence state is the zero magnetic flux state after the magnetic core has completed standard demagnetization. The standard demagnetization method is as follows: apply a 50Hz alternating current with a peak value gradually decaying to 0 to the excitation winding, with a decay period ≥10, and the final remanence ≤1%×B. s ×A e To ensure consistency in the cumulative starting point of each monitoring cycle; Φ0 is the residual magnetic flux after demagnetization, defaulting to 0 Wb; k1 is a constant related to the equivalent series resistance of the electrolytic capacitor, and its complete calculation formula is: , Where ESR is the equivalent series resistance of the electrolytic capacitor at a reference frequency of 1kHz, and its unit is ohms (Ω); V core ρ represents the core volume of the electrolytic capacitor, in cubic meters (m³); ρ is the volumetric heat capacity of the electrolyte in the electrolytic capacitor, in joules per cubic meter at degrees Celsius (J / (m³・℃)), typically taken as 1.4 × 10⁻⁶. 6 ~1.6×10 6 J / (m³・℃;C th This represents the maximum allowable steady-state temperature rise of the electrolytic capacitor, expressed in degrees Celsius (°C), typically ranging from 30°C to 50°C. k2 is a constant related to the accumulated core's magnetic circuit parameters; the complete formula for calculating k2 is: , Where μ0 is the free permeability, with a value of 4π × 10⁻⁶. −7 Henry / meter (H / m); μ r A represents the cumulative average relative permeability of the core in the unsaturated operating region. e The cumulative effective cross-sectional area of ​​the magnetic core is expressed in square meters (m²); Le The cumulative effective magnetic circuit length of the magnetic core is expressed in meters (m).

[0065] The irreversible hysteresis accumulation and triggering characteristics of this embodiment are as follows: Figure 3 As shown.

[0066] Depend on Figure 3 It is evident that when the magnetic field strength generated by the driving pulse energy is lower than the coercivity of the accumulating magnetic core, the accumulating magnetic core operates in the reversible magnetization region with no net magnetic flux accumulation. When the magnetic field strength exceeds the coercivity, the magnetic flux accumulates irreversibly in a step-like manner and remains unchanged after power is cut off. When the accumulated magnetic flux reaches the preset magnetic saturation threshold, due to the sharp drop in the differential permeability of the magnetic core, the output voltage of the detection winding will generate a step jump, exceeding the opening threshold of the switching device, thereby reliably triggering the protection action.

[0067] After matching, the protection triggering accuracy can be verified using the following methods: A programmable DC power supply outputs a continuous pulse of rated ripple current, while a fluxmeter monitors the accumulated magnetic flux change of the core, and an LCR meter measures the ESR and capacitance change of the electrolytic capacitor in real time; when the accumulated magnetic flux reaches Φ... th At that time, the actual damage calculated based on the ESR change rate and capacity decay rate is different from the preset D. th The deviation should be ≤ ±10%; if the deviation exceeds the range, it can be corrected by fine-tuning the number of turns in the excitation winding or the turns ratio of the inductive coupling element.

[0068] Once the core parameters are determined, the cumulative characteristics can be verified using the following method: apply unipolar pulses of different amplitudes and widths, measure the change in magnetic flux after each pulse, and verify the relationship between the net magnetic flux increment per pulse and H. exceed The linear relationship between ×Δt; apply continuous pulses with the same parameters and measure the linear relationship between the cumulative magnetic flux and the number of pulses; after the accumulated magnetic core is de-energized and placed for 72 hours, measure the magnetic flux again to verify that the magnetic flux retention rate is ≥99%; if the linearity does not meet the requirements, the working magnetic flux density of the magnetic core can be adjusted to 20%~30% of the saturation magnetic flux density.

[0069] This embodiment clarifies the critical conditions and quantitative mapping relationship for irreversible hysteresis accumulation, and establishes a one-to-one mathematical model of the cumulative magnetic flux and the cumulative thermal damage of the electrolytic capacitor. By recording damage information through the residual magnetism of the magnetic core, continuous and uninterrupted damage accumulation can be achieved throughout the entire life cycle of the system. At the same time, the coercivity characteristics of the magnetic core are used to automatically filter out harmless background ripples, providing inverse time protection characteristics.

[0070] In one feasible implementation, in step S2, the excitation windings of multiple groups of cumulative magnetic cores with different coercivity parameters are connected in parallel to the same excitation circuit, and each group of cumulative magnetic cores responds to ripple events with different amplitude ranges. In step S3, by monitoring the saturation timing and combination state of each group of cumulative magnetic cores, a piecewise fitting of the electrolytic capacitor damage curve is achieved.

[0071] In step S2, a negative temperature coefficient thermistor is connected in series in the excitation circuit. By utilizing the characteristic that the resistance of the negative temperature coefficient thermistor decreases as the temperature rises, the magnitude of the excitation current is automatically adjusted so that the net magnetic flux increment generated by a single ripple event increases as the temperature rises, thereby adaptively matching the magnetic flux accumulation rate with the temperature-related damage acceleration characteristics of the electrolytic capacitor.

[0072] In step S3, the amplitude of the voltage spike induced by the detection winding is not lower than the gate turn-on threshold voltage of the switching device; when the accumulated magnetic core has not reached the magnetic saturation threshold, the amplitude of the induced voltage generated by the normal ripple event in the detection winding is insufficient to trigger the switching device to turn on.

[0073] The method further includes step S5: after disconnecting the DC bus power supply and completing the fault investigation, a reverse current pulse is applied to the excitation winding of the accumulated magnetic core to restore the magnetic flux of the accumulated magnetic core from the state of reaching the magnetic saturation threshold to the initial residual magnetism state.

[0074] In this embodiment, segmented fitting refers to performing multi-segment linear fitting on the electrolytic capacitor damage curve by using different coercive magnetic cores to respond to different amplitude ripples, with a fitting degree of ≥98% across the entire amplitude range.

[0075] Temperature adaptive compensation is achieved through a negative temperature coefficient (NTC) thermistor. Utilizing the characteristic that its resistance changes with temperature, the excitation current is automatically adjusted. The NTC thermistor can be placed at any location capable of sensing the operating temperature of the electrolytic capacitor, such as close to the capacitor's outer casing or embedded in the capacitor mounting base. In this embodiment, the NTC thermistor is tightly attached to the center of the top of the electrolytic capacitor's outer casing, ensuring no air gaps. The temperature deviation between the temperature sampling and the capacitor's core temperature is ≤5℃. The temperature characteristic of the resistance change matching the electrolytic capacitor's damage rate satisfies the formula: , In the formula, RT is the resistance of the NTC thermistor at thermodynamic temperature T, in ohms (Ω); R 25 T represents the nominal resistance of the NTC thermistor at 25°C, in ohms (Ω); B is the material constant of the NTC thermistor, in Kelvin (K); T is the current thermodynamic temperature, in Kelvin (K). 25The temperature corresponding to 25℃ is the thermodynamic temperature, expressed in Kelvin (K). A reverse reset current pulse indicates that the amplitude of the generated reverse magnetic field is ≥2 times the core coercivity, ensuring the core returns to its initial remanent magnetization state and enabling the device to be reused.

[0076] In this embodiment, the multi-core parallel segmented fitting is implemented as follows: the excitation windings of the three sets of cumulative magnetic cores are connected in parallel and then in series to the excitation circuit to ensure that the same excitation current flows synchronously through each set of windings; the coercivity parameters are as follows: low coercivity magnetic core H c1 =5A / m, response 1.05~1.2 times rated ripple; medium coercivity core H c2 =15A / m, response 1.2~2 times rated ripple; high coercivity core H c3 =30A / m, with a response of more than twice the rated ripple, where H c1 H c2 H c3 The values ​​represent the coercivity of low, medium, and high coercivity magnetic cores, respectively, all in amperes per meter (A / m).

[0077] Each set of magnetic cores has an independently wound detection winding. The output is connected to the driving terminal of the switching device after being combined with a Schottky diode or logic gate. Protection can be triggered when any set of magnetic cores reaches the threshold.

[0078] In temperature adaptive compensation, the NTC is connected in series in the excitation circuit. At 25℃, the nominal resistance is 30%~50% of the total equivalent resistance of the excitation circuit at 25℃, and the B value is 3500K~4000K, which matches the life temperature characteristics of the electrolytic capacitor. When the temperature rises, the NTC resistance decreases, the excitation current increases, the accumulation rate accelerates, and the protection triggers earlier. When the temperature drops, the resistance increases and the accumulation rate slows down, realizing adaptive protection across the entire temperature range.

[0079] During trigger signal generation, the detection winding and the excitation winding are wound in the same direction, with the number of turns being 0.3 to 0.8 times that of the excitation winding. The output terminal of the detection winding is connected in series with a Schottky rectifier diode and a current-limiting resistor, and then connected to the gate of the switching device. The anode of the Schottky diode is connected to one end of the detection winding, and the cathode is connected to the current-limiting resistor to ensure that only forward voltage spikes can act on the gate and that reverse voltage is blocked. At the same time, a Zener diode is connected in parallel between the gate and the source to limit the maximum gate voltage. When the magnetic core is not saturated, the induced voltage of the detection winding is ≤1V, which is lower than the switching device turn-on threshold. When the accumulated magnetic core reaches the magnetic saturation threshold, the amplitude of the induced voltage increases by more than 5 times, which can reliably drive the switching device to conduct.

[0080] The criteria for determining whether a reset is complete are as follows: after the reset pulse is removed, the deviation between the induced voltage of the detection winding under the standard excitation pulse and the induced voltage under the initial demagnetization state is ≤±3%, ensuring that the magnetic core is completely restored to the initial zero flux state; the duration of the reset pulse is 10ms~50ms, and the reverse magnetic field strength corresponding to the pulse amplitude is ≥2×H. c To ensure complete reversal and reset of the magnetic domains, a reset branch is connected in parallel across the excitation winding. This branch consists of a reset button, a DC power supply, and a current-limiting resistor connected in series. The polarity of the power supply is opposite to that of the excitation pulse. The current-limiting resistor value satisfies the requirement that the magnetic field strength generated by the reverse current is ≥ 2 times the coercivity of the magnetic core. After troubleshooting, pressing the reset button applies a 10ms~50ms reverse current pulse to complete the magnetic core reset, and the device enters the next monitoring cycle.

[0081] This embodiment, while maintaining a fully passive architecture, further expands the operating condition adaptability of the method; through a segmented fitting technique using multiple sets of parallel coercive magnetic cores, it achieves a fitting degree of ≥98% for the electrolytic capacitor damage curve across the entire amplitude range; through NTC temperature adaptive compensation technology closely attached to the electrolytic capacitor, it automatically matches the temperature-accelerated aging characteristics of the electrolytic capacitor; and by combining a passive triggering mechanism for a sharp drop in permeability with a resettable hysteresis accumulation design, it achieves repeatable execution of the method, improving its engineering practicality.

[0082] The above description is merely a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the concept described herein through the above teachings or related technologies or knowledge. Modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims.

Claims

1. A DC ripple adaptive monitoring and protection method based on hysteresis accumulation, used for ripple damage monitoring and protection of DC bus electrolytic capacitors, characterized in that, Includes the following steps: S1: The primary winding of the inductive coupling element is connected in series with the DC bus, and the ripple component in the bus current is extracted through the secondary winding, which is magnetically coupled to the primary winding. The inductive coupling element uses the physical loss characteristics of its own magnetic core to perform passive frequency compensation on the extracted ripple component and outputs drive pulse energy. The characteristic of the drive pulse energy of the ripple component at different frequencies changing with frequency is matched with the characteristic of the equivalent series resistance loss power of the electrolytic capacitor changing with the ripple frequency, and the fitting degree is not less than 95% across the entire frequency band. S2: The driving pulse energy is applied to the excitation winding that is magnetically coupled to the accumulating magnetic core. The excitation winding, the rectifier element and the secondary winding of the inductive coupling element are connected in series to form an excitation circuit, so that the driving pulse applied to the excitation winding is unipolar. The excitation winding generates a unipolar magnetic field strength pulse in the accumulating magnetic core with rectangular hysteresis loop characteristics, driving the magnetic flux of the accumulating magnetic core to generate an irreversible net magnetic flux increment from the current remanent state to the saturation magnetic flux direction, and maintaining the accumulated magnetic flux state by relying on the remanence after the pulse disappears. S3: The magnetic flux state is monitored by the detection winding magnetically coupled to the accumulated magnetic core. When the accumulated magnetic flux reaches the preset magnetic saturation threshold, the characteristic of the accumulated magnetic core's permeability dropping sharply, which leads to an increase in the excitation current change rate, is used to generate a voltage spike in the detection winding that is 5 times or more higher than the induced voltage amplitude when the accumulated magnetic core has not reached the magnetic saturation threshold, as a trigger signal. S4: In response to the trigger signal, drive the switching device to cut off the DC bus power supply.

2. The DC ripple adaptive monitoring and protection method based on hysteresis accumulation according to claim 1, characterized in that, The passive frequency compensation step in step S1 includes: The magnetic core material whose loss tangent increases with increasing frequency is selected as the magnetic core of the inductive coupling element. This makes the magnetic core loss generated by the higher frequency ripple component in the magnetic core greater, and the corresponding drive pulse energy output by the secondary winding attenuation greater. This matches the characteristic that the equivalent series resistance loss of the electrolytic capacitor decreases with increasing ripple frequency. A compensation resistor is connected in parallel at the output terminal of the secondary winding of the inductive coupling element. By adjusting the resistance value of the compensation resistor, the characteristic of the driving pulse energy output by the inductive coupling element changing with the ripple frequency under the same ripple current amplitude is matched with the characteristic of the power loss of the equivalent series resistance of the electrolytic capacitor changing with the ripple frequency.

3. The DC ripple adaptive monitoring and protection method based on hysteresis accumulation according to claim 2, characterized in that, The value of the compensation resistor is selected to satisfy the following condition: within the range of ripple frequency variation of the electrolytic capacitor, the time integral value of the driving pulse energy and the time integral value of the power loss of the equivalent series resistance of the electrolytic capacitor maintain a fixed preset ratio.

4. The DC ripple adaptive monitoring and protection method based on hysteresis accumulation according to claim 1, characterized in that, The irreversible net flux increment mentioned in step S2 is achieved in the following way: A high remanence ratio rectangular hysteresis loop soft magnetic material is selected as the accumulation core. When the magnetic field strength generated by the driving pulse energy exceeds the coercivity of the accumulation core, the domain walls inside the core undergo irreversible displacement. After the magnetic field is removed, the core stabilizes at a new remanence point, generating a net magnetic flux increment corresponding to a single ripple event. Under multiple ripple events, the cumulative magnetic flux is the sum of the net magnetic flux increments of each event. The cumulative magnetic flux is positively correlated with the total cumulative damage of the electrolytic capacitor. The cumulative magnetic flux is maintained by the residual magnetism after the DC bus is de-energized, and the magnetic flux retention rate is not less than 99% after the DC bus is de-energized for at least 72 hours.

5. The DC ripple adaptive monitoring and protection method based on hysteresis accumulation according to claim 4, characterized in that, The cumulative damage D of the electrolytic capacitor satisfies ， Where n is the total number of ripple events within the statistical time period; I ripple,i Δt represents the effective value of the ripple current corresponding to the i-th ripple event. 1,i is the duration of the i-th ripple event; k1 is a constant related to the equivalent series resistance, thermal resistance, and aging characteristics of the electrolytic capacitor; The magnetic flux accumulation Φ satisfies ， Where n is the total number of ripple events within the statistical time period; H exceed,i For the i-th ripple event, exceeding the core coercivity H c The magnetic field strength component, i.e. ； H i H represents the instantaneous magnetic field strength generated by the excitation winding in the accumulating core during the i-th ripple event; c The coercivity of the magnetic core at the operating temperature; Δt 2,i For the i-th ripple event, H exceed,i The total duration of a continuous time interval >0; k2 is a constant related to the properties of the magnetic core material and the magnetic circuit parameters; When the accumulated magnetic flux Φ reaches the preset magnetic saturation threshold Φ th When the cumulative damage D of the electrolytic capacitor reaches the preset protection limit value D, th This ensures that the protection trigger time corresponds to the actual degree of damage to the electrolytic capacitor.

6. The DC ripple adaptive monitoring and protection method based on hysteresis accumulation according to claim 1, characterized in that, In step S2, the excitation windings of multiple groups of accumulator cores with different coercivity parameters are connected in parallel to the same excitation circuit, and each group of accumulator cores responds to ripple events with different amplitude ranges. In step S3, by monitoring the saturation timing and combination state of each group of accumulator cores, a piecewise fitting of the electrolytic capacitor damage curve is achieved.

7. The DC ripple adaptive monitoring and protection method based on hysteresis accumulation according to claim 1, characterized in that, In step S2, a negative temperature coefficient thermistor is connected in series in the excitation circuit. By utilizing the characteristic that the resistance of the negative temperature coefficient thermistor decreases as the temperature rises, the magnitude of the excitation current is automatically adjusted so that the net magnetic flux increment generated by a single ripple event increases as the temperature rises, thereby adaptively matching the magnetic flux accumulation rate with the temperature-related damage acceleration characteristics of the electrolytic capacitor.

8. The DC ripple adaptive monitoring and protection method based on hysteresis accumulation according to claim 1, characterized in that, In step S3, the amplitude of the voltage spike induced by the detection winding is not lower than the gate turn-on threshold voltage of the switching device; when the accumulated magnetic core has not reached the magnetic saturation threshold, the amplitude of the induced voltage generated by the normal ripple event in the detection winding is insufficient to trigger the switching device to turn on.

9. The DC ripple adaptive monitoring and protection method based on hysteresis accumulation according to claim 1, characterized in that, The method further includes step S5: After disconnecting the DC bus power supply and completing the fault diagnosis, a reverse current pulse is applied to the excitation winding of the accumulated magnetic core to restore the magnetic flux of the accumulated magnetic core from the state of reaching the magnetic saturation threshold to the initial residual magnetism state.

10. The DC ripple adaptive monitoring and protection method based on hysteresis accumulation according to claim 4, characterized in that, When the magnetic field strength generated by the driving pulse energy does not exceed the coercivity of the accumulating magnetic core, the accumulating magnetic core operates in the reversible magnetization range and does not generate net magnetic flux accumulation.

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