91 results about "Dc bus capacitor" patented technology

The invention, which belongs to the technical field of the energy storage converter, discloses an electrical parameter sensing-based service life monitoring system for a capacitor of a network-forming type energy storage converter, comprising the following steps of: synchronously acquiring a direct-current voltage signal and a three-phase alternating-current signal of a direct-current bus capacitor through an electrical parameter acquisition module to form a multi-dimensional feature vector; a state observer built in the ESR estimation module is used for analyzing the signal, a target capacitor ESR value is obtained, and a capacitor core temperature value is obtained through back-stepping through an electric-thermal coupling field analysis model of a core temperature back-stepping module in combination with preset capacitor surface temperature data; based on the ESR value and the capacitor core temperature value, a life prediction module calculates the residual life and health degree index of the capacitor; and the power scheduling module executes capacitor health degree-power output joint scheduling according to the health degree index, adjusts the power fluctuation range of the converter, and feeds back real-time working condition data to the electrical parameter acquisition module, thereby realizing accurate monitoring of the capacitor state and intelligent scheduling of the converter power.

The embodiment of the invention provides a wind power converter DC bus capacitor state monitoring system and method, and the method comprises the steps: firstly introducing a physical model of a capacitor temperature, and carrying out the decoupling compensation of a preliminarily estimated equivalent series resistor, so as to effectively strip the measurement disturbance caused by the fluctuation of an operation temperature; on the basis, working condition data such as active power of the converter are further fused, and a health baseline capable of being dynamically and adaptively adjusted along with the operation working condition is established as a judgment standard. And finally, comparing the equivalent series resistor subjected to multiple correction with the self-adaptive healthy baseline in real time, so as to accurately identify inherent performance degradation caused by self aging of the capacitor. In this way, interference of complex and changeable working conditions on monitoring results can be overcome, and therefore the accuracy and reliability of state evaluation are remarkably improved.

The utility model discloses a seven-level inverter topology, which relates to the technical field of multi-level structures and comprises an upper bridge arm and a lower bridge arm, the upper bridge arm and the lower bridge arm are mutually symmetrical except for the direction of a diode, and a plurality of switch tubes, direct current bus capacitors and flying capacitors in the upper bridge arm and the lower bridge arm are connected according to a specific rule. Working modes with seven different output voltages are realized by controlling the conduction state of the switch tube; the topology realizes voltage division through the DC bus capacitor, realizes intermediate level transition through the flying capacitor, combines an optimized circuit structure and a control strategy, has the advantages of simple circuit design, high efficiency, stable output voltage and the like, and is widely applicable to high-voltage and high-power inverter systems.

This invention discloses a transient control method for a wind turbine grid-connected system that utilizes a reverse energy absorption branch, relating to the field of new energy technology. The energy-consuming branch is connected in parallel to the DC bus capacitor. The grid connection point voltage and DC bus voltage of the wind turbine grid-connected system are acquired. When the grid connection point voltage reaches a preset condition, a reference value for the d-axis current of the grid-side converter is calculated based on the grid connection point voltage and the voltage of the DC bus capacitor. Based on the reference value, the active power state of the grid-side converter is switched to an active power absorption state, allowing the DC bus capacitor to store electrical energy and raise the voltage. When the voltage of the DC bus capacitor is greater than the threshold voltage of the transistor, the transistor is controlled to be in the conducting state. Through this technical solution, the direction of energy flow on the DC bus between the turbine-side converter and the grid-side converter can be changed. Furthermore, by consuming excess energy through resistance, wind turbine output oscillations and DC-side overvoltage can be suppressed, and the synchronous stability of the wind turbine grid-connected system can be improved.

The application provides a power converter, a controller, a power supply system and a midpoint voltage deviation control method, which are applied to the technical field of power electronics, and the power converter comprises a power conversion module, a main control module and at least two DC bus capacitors, each DC bus capacitor is connected in series between the positive electrode of a DC bus and the negative electrode of the DC bus, and since the midpoint voltage deviation suppression strategy in the related art can only achieve good midpoint deviation suppression effect when the bus voltage is high, the main control module increases the bus voltage when the voltage deviation between the capacitance voltage of at least one DC bus capacitor and the target capacitance voltage is greater than the first preset deviation threshold, thereby providing guarantee for the midpoint voltage deviation suppression strategy to achieve better midpoint deviation suppression effect, improving the midpoint deviation suppression effect and significantly improving the stability of the power supply system.

This invention discloses a control method for a cascaded photovoltaic inverter under phase-to-phase short-circuit fault conditions in the power grid, belonging to photovoltaic power generation technology in the field of electrical engineering. The steps are as follows: First, determine the fault type of the three-phase power grid and detect the ratio of the line voltage amplitude of the two faulty phases after the voltage drop to that of the two faulty phases before the voltage drop. Then, use a proportional resonant controller to control the grid-connected current. Second, adopt an adaptive zero-sequence voltage compensation control strategy based on active current injection to adaptively compensate the zero-sequence voltage according to the maximum positive-sequence active current actually output by the inverter. Third, control the average value of the DC bus capacitor voltage of the H-bridge converter by controlling a two-level full-bridge LLC converter with one input and m outputs. When a phase-to-phase short-circuit fault occurs in the power grid, this control method improves the adaptability of the cascaded photovoltaic grid-connected inverter to different output power and different grid voltage drop depths, and improves the system's low-voltage ride-through capability.

This invention provides a three-phase isolated bidirectional AC-DC converter and a component monitoring method, relating to the field of AC-DC converter technology. It includes a three-phase full-bridge circuit, a resonant network circuit, an output rectifier circuit, a status monitoring circuit, and a controller. The three-phase full-bridge circuit includes an A-phase bridge arm unit, a B-phase bridge arm unit, and a C-phase bridge arm unit, with the three-phase output power supply connected to each unit respectively. The resonant network circuit is connected to the three-phase full-bridge circuit, and the output rectifier circuit is also connected to the resonant network circuit. The controller is communicatively connected to the switching transistors in the three-phase full-bridge circuit. A temperature monitoring unit is connected to the switching transistors in the three-phase full-bridge circuit. This invention reduces the number of switching transistors in the converter, reduces the adjustment pressure on the DC side, and decreases the size of the DC bus capacitor, thereby reducing the complexity of the converter and decreasing the possibility of prolonged operation under fault conditions.

This invention discloses a system for reducing the ripple current of a DC bus capacitor, comprising a DC bus capacitor C1, an inverter circuit, a current sampling circuit, an energy storage inductor L1, and a control circuit. This invention also discloses a method for reducing the ripple current of a DC bus capacitor. In this invention, an energy storage inductor L1 is placed between the positive terminal of the battery and the positive terminal of the DC bus capacitor C1. The control circuit controls the energy storage inductor L1 to charge or discharge to the motor according to the direction and magnitude of the current flowing through the DC bus capacitor C1, thereby reducing the charging or discharging current of the DC bus capacitor C1, and consequently reducing the ripple current of the DC bus capacitor C1. This reduces the temperature rise of the DC bus capacitor during operation, thereby extending the service life of the DC bus capacitor C1. This invention also features a simple structure, low cost, and high reliability.

The invention relates to an MMC-based multi-terminal interlaced direct current power flow controller, which comprises an MMC circuit and a control module which are connected with each other, the MMC circuit is a multi-port network and comprises a direct current bus capacitor and a converter which are connected with each other, the converter comprises converter branches of which the number is the same as that of ports, and the converter branches are connected with the control module. Each converter branch comprises an upper arm and a lower arm which are connected to the midpoint of the converter branch, the midpoint of each converter branch provides the port outwards, and each arm comprises N submodules which are in cascade connection, the control module obtains PWM pulse signals of the sub-modules through external power flow control, internal power flow control and module capacitance balance control. Compared with the prior art, power distribution control among multiple power transmission lines in the high-voltage direct-current power transmission network is realized, and the method has the advantages of higher output voltage level, stronger robustness, less alternating-current component injection in the power transmission lines and the like.

Embodiments of the present disclosure disclose Variable-frequency Drive (VFD) and motor drive system. The VFD comprising a three-level rectifier, coupled with a three-phase power supply; an even number of direct-current (DC) bus capacitors, coupled with the three-level rectifier; and a H-bridge inverter, coupled with the even number of DC bus capacitors; wherein the H-bridge inverter comprises a first bridge arm and a second bridge arm, an output midpoint of the three-level rectifier is coupled with a midpoint of the even number of DC bus capacitors, the midpoint of the even number of DC bus capacitors is coupled with a first input terminal of a three-phase motor, a midpoint of the first bridge arm is coupled with a second input terminal of the three-phase motor, and a midpoint of the second bridge arm is coupled with a third input terminal of the three-phase motor. H-bridge inverter containing two bridge arms is used to drive three-phase motor, reducing the number of power switches and saving component costs..

The embodiment of the invention provides a DC micro-grid stability control method considering a constant power load, and relates to the technical field of power electronic equipment, and the method comprises the steps: building a state space model of a Boost DC-DC converter; constructing a linear active disturbance rejection controller; dC bus capacitor voltage is collected as a capacitor voltage measurement value; estimating the total disturbance of the system, and outputting a total disturbance observation value; the state feedback control unit executes duty ratio signal generation and output; discretization reconstruction is carried out on the linear active disturbance rejection controller, and a discretization control algorithm adaptive to the digital control chip is generated; capacitor voltage acquisition, disturbance observation value updating and duty ratio signal output are circularly completed according to a set sampling period. The technical problems that in the prior art, control parameters are generally designed and optimized based on a small signal model, large-range disturbance cannot be dealt with, the system is unstable under the large disturbance condition, and the reliability and safety of the micro-grid are seriously affected are solved.

The invention provides a string photovoltaic inverter bus capacitor on-line monitoring and life warning method and device, and the method comprises the steps: 1, controlling a discharge loop of a photovoltaic inverter system to discharge a DC bus capacitor after an inverter is shut down at night; step 2, acquiring attenuation data of bus voltage in a discharging process, and calculating an actual capacitance value of a direct-current bus capacitor through a preset fault prediction and health management algorithm according to the attenuation data; 3, comparing the actual capacitance value with a preset reference capacitance value to calculate the health degree of the direct current bus capacitor; and when the health degree is lower than a preset alarm threshold value, generating and sending out a life alarm signal. According to the method, existing hardware and night working conditions of the inverter are fully utilized, additional detection equipment does not need to be added, online and automatic monitoring and accurate service life evaluation of the bus capacitor capacitance value are achieved, and the problem that an effective online monitoring means is lacked in traditional operation and maintenance is effectively solved.

The application discloses a control method and device of a vehicle-mounted charger, a vehicle-mounted charging system and a vehicle, and relates to the technical field of vehicle-mounted charging. The control method comprises the following steps: through controlling the action of the secondary side power switch tube of the isolation type DC / DC circuit in the vehicle-mounted charger, the pre-charging process of the DC bus capacitor is realized by using the electric energy of the power battery to charge the DC bus capacitor; the soft start of the isolation type DC / DC circuit is realized by gradually increasing the duty cycle at the start time, the oscillation of the resonance current is avoided, and the smoothness of the charging voltage output to the DC bus capacitor is improved; meanwhile, the loss in the isolation type DC / DC circuit is reduced by reducing the switching frequency after the duty cycle is stable, so that the gain of the output charging voltage is improved, and the fast charging of the DC bus capacitor is realized. The whole pre-charging process is realized by reusing the isolation type DC / DC circuit in the vehicle-mounted charger, no additional hardware is needed, and the application cost of the vehicle-mounted charger is effectively saved.

The invention provides a three-level neutral-point-clamped bridge arm switch unit integrated structure, and relates to the technical field of multi-level bridge arm circuits. The circuit comprises a bottom copper-clad ceramic substrate, a top copper-clad ceramic substrate and a printed circuit board, the bottom copper-clad ceramic substrate bears half of the three-level bridge arm circuit, and the top copper-clad ceramic substrate bears the other half of the three-level bridge arm circuit; the printed circuit board bears a direct current bus capacitor and is electrically connected with the bottom copper-clad ceramic substrate and the top copper-clad ceramic substrate. Compared with a discrete component or a single-sided power module, the integrated structure provided by the invention has the advantages that the lead area is shortened, the occupied total area is smaller, and the magnetic field / inductance parameter induced by the circuit is lower, so that the parasitic inductance of the commutation loop is reduced by virtue of the extremely small integrated area and the commutation loop structure, and the safety of the three-level converter is further improved.

This invention belongs to the field of microgrid inertia simulation technology. It proposes a distributed inertia simulation method and system for hybrid AC / DC microgrids. The system is built around a closed-loop logic of "frequency information without communication transmission - adaptive high-precision sensing - nonlinear inertia accurate output - IPSO optimized multi-topology aggregation - overall system stable control". A reference value is constructed by superimposing an AC disturbance signal onto the rated voltage of the DC bus. The average value of this disturbance signal is zero, so the steady-state DC component of the DC bus voltage is not changed, keeping it stable near the rated value. The DC bus capacitor only serves as a medium for transmitting frequency information and does not participate in energy storage and release. This solves the voltage deviation problem caused by energy release and absorption in traditional capacitor inertia simulation methods, avoids the risk of overvoltage / undervoltage protection actions and system instability caused by this, and ensures the stability of system operation.

The utility model provides a pulse power supply which comprises an even number of pulse power units, every two pulse power units are arranged in a mirror symmetry mode, each pulse power unit comprises a direct current bus capacitor, a power electronic switch device, a follow current circuit, a laminated busbar and a first output copper bar, and the direct current bus capacitors are installed on the laminated busbar; the first end of the electronic power switch device is installed on the positive electrode bar of the laminated busbar, and the second end of the electronic power switch device is connected with the first output copper bar. The follow current circuit is installed close to the power electronic switching device and is connected between the negative electrode bar of the laminated busbar and the second end of the power electronic switching device, and the first output copper bar and the negative electrode bar of the laminated busbar are respectively connected with a load through a conductor. The length of the line between the power electronic switching device and the follow current circuit is greatly reduced, so that the parasitic inductance generated by the line is greatly reduced, and the peak voltage is further reduced.

The invention relates to the technical field of power electronics, and discloses a non-load loop hybrid multi-level converter pre-charging control system and method.The pre-charging circuit is provided with an auxiliary switch, an anode main switch and a pre-charging resistor, and the auxiliary switch and the pre-charging resistor are connected in series and bridged between the anode of a direct-current power source and the anode of a direct-current bus capacitor bank; the positive pole main switch is connected in parallel; the direct current bus capacitor bank is composed of series bus capacitors; each phase of the A-phase bridge arm, the B-phase bridge arm and the C-phase bridge arm is provided with four groups of main switches and corresponding flying capacitors. The control module turns off all the switches in an initial power-on state, the auxiliary switch is firstly closed and a three-phase upper bridge arm specified switch is turned on during pre-charging, so that the direct-current bus capacitor bank and the three flying capacitors share a pre-charging resistor for parallel charging, and then the switches are controlled in stages according to the voltages of the flying capacitors and the direct-current bus capacitors. The problems that an existing pre-charging technology increases the size and cost of a converter and highly depends on an output side load are solved.

The embodiment of the invention discloses a low-voltage flexible direct-current power supply system and a soft start control method, and the method comprises the steps: controlling a direct-current bus circuit breaker to be closed under the condition that switch driving signals of a rectifier and an inverter are in a locking state, and building the electrical connection between the rectifier and the inverter; controlling a first alternating-current bus circuit breaker to be closed, charging two direct-current bus capacitors through a charging resistor, and controlling a bypass switch of the charging resistor to be closed if the direct-current bus voltage reaches a first expected voltage; and controlling the rectifier to operate in a closed-loop control mode so as to adjust the direct-current bus voltage, if the direct-current bus voltage reaches a second expected voltage, controlling the second alternating-current bus circuit breaker to be closed, and controlling the active power reference value to be gradually increased to a target power value along with time. According to the technical scheme provided by the embodiment of the invention, the cost and the size of hardware can be reduced, and under / over-voltage and over-current conditions in the starting process can be effectively avoided.

The invention belongs to the technical field of power electronic converter optimization design. In order to solve the problems that an existing T-type three-level converter direct-current bus capacitor capacitance value calculation model is rough, influences of high and low frequency ripples are not distinguished, and the design margin is too large, the method comprises the steps that a ripple voltage analysis model is constructed, ripple current is decomposed into low-frequency and high-frequency components, and it is clear that the high-frequency component is a voltage fluctuation core; analyzing a high-frequency ripple microcosmic change rule, and deducing a fluctuation expression; introducing a modulation degree and a power factor to construct a full-working-condition extremum function, and optimizing a worst working condition point and a maximum ripple coefficient; and in combination with the voltage stabilization precision index and the rated parameter, the minimum capacitance value meeting the requirement is deduced, and accurate type selection is realized.

The invention relates to a capacitance value determination method for a DC bus capacitor of a multiplex power converter. Under the condition that the initialized capacitance value of the direct-current bus capacitor in the multiplexing power converter meets a constraint condition, determining a first ripple current of the direct-current bus capacitor of the multiplexing power converter in a direct-current working mode based on the initialized capacitance value, determining a second ripple current of a direct current bus capacitor of the multiplexing power converter in the alternating current working mode based on the initialized capacitance value; determining a comparison result between the rated ripple current of the DC bus capacitor and the first ripple current and the second ripple current; determining a target optimization value according to a comparison result; and updating the initialized capacitance value according to the target optimization value to obtain a target capacitance value of the DC bus capacitor. According to the embodiment of the invention, the target capacitance value is determined by fully considering the collaborative characteristic of the double-side ripple current, so that frequent determination of the direct-current bus capacitance is avoided, and the cost of the multiplexing power converter is reduced.

This invention belongs to the field of power electronics and DC power system protection technology, specifically relating to a boost converter topology and control method. The structure includes: a power supply and a boost inductor L. boost Main switch tube Q 1. Converter circuit breaker Q conv capacitor circuit breaker Q cap The components include a first resistor R1, a second resistor R2, a load resistor R3, a first capacitor C1, a second capacitor C2, a third capacitor C3, a first diode Dsnub1, a second diode Dsnub2, a varistor MOV, and a line inductor Lline. This invention can replace traditional DC circuit breakers, improving system operating efficiency and protection performance. It can interrupt the discharge current of the DC bus capacitor in microseconds and safely release the inductor's stored energy in milliseconds, avoiding voltage overshoot in semiconductor devices and effectively improving the safety and reliability of the DC power grid.

The invention discloses a three-level active power filter direct-current bus capacitor design method and system, and belongs to the field of power electronic device design, and the method comprises the steps: determining the minimum capacity demand of a direct-current bus capacitor according to the rated power of a system and the working condition of a power grid; respectively calculating effective values of the triple frequency ripple current and the high-frequency ripple current related to the switching frequency by adopting a decomposition analysis method of a low-frequency component and a high-frequency component; by decomposing the low-frequency ripple current and the high-frequency ripple current, a ripple current mathematical model is established to analyze the bearing capacity of the capacitor for ripple current of different frequencies, and model selection and parallel configuration of the capacitor are obtained; carrying out the structure and heat dissipation design of the capacitor; evaluating the service life of the capacitor, and designing a maintenance mechanism in combination with a service life evaluation result; simulation verification is carried out, the current ripple control effect is tested firstly, and then the system stability is verified. The method optimizes the parallel configuration of the capacitors, and improves the dynamic response performance and long-term operation reliability of the system.

The invention provides a zero sequence excitation boost type hybrid excitation synchronous motor and a driving topology thereof, a motor controller and a design method thereof, the driving topology comprises a direct current bus capacitor, a three-phase inverter, a three-phase armature winding and an excitation winding, one end of the direct current bus capacitor is connected with a common anode of the three-phase inverter, and the other end of the direct current bus capacitor is connected with a common cathode of the three-phase inverter; one end of the armature winding is connected with a common cathode of the three-phase inverter, the other end of the armature winding is connected with a common cathode and a grounding end of the three-phase inverter and serves as a negative terminal to be connected with a negative electrode of a direct-current power supply of the motor, the output end of each phase bridge arm of the three-phase inverter is connected with one end of each phase armature winding, and the other ends of the phase armature windings are mutually connected to form a neutral point. One end of the excitation winding is directly connected with the neutral point, and the other end of the excitation winding serves as a positive terminal to be connected with the positive electrode of a direct-current power supply of the motor. The driving topology provided by the invention has the capability of boosting the input voltage of the power supply while exciting the excitation winding, and the performance of the hybrid excitation synchronous motor is remarkably improved.

The invention discloses a fault detection method and system for a driving circuit of an electronic circuit board, and relates to the technical field of electronic engineering. According to the fault detection method for the electronic circuit board driving circuit, impedance spectrum scanning, switch stress pulse and dynamic response test signals are injected into the electronic circuit board driving circuit in sequence, response signals are collected, and the impedance characteristic, the resonance mode and the dynamic performance of the circuit are analyzed. The capacitance value and the equivalent series resistance of a direct current bus capacitor are obtained through impedance analysis, the dominant resonant frequency and the damping ratio of a power loop are obtained through resonance mode analysis, and the phase margin of a control loop is obtained through dynamic performance analysis. According to the method, impedance, resonance and control parameters are extracted through multi-signal injection, fault diagnosis reliability and accuracy are improved through combined analysis, and stable operation of a system is guaranteed.

A method to estimate a remaining of useful life of a DC link capacitor of a converter through determination of a minimum value Clim of its capacitance C under which performances of the converter are considered as insufficient. The method includes implementing a real time model including a motor drive model and a capacitor model using decreasing capacitor values to calculate a forecasted minimum capacitance Clim sufficient for keeping at least one of DC voltage ripple, motor current ripple, speed ripple or torque ripple under a specified value. The method further includes calculating a time difference between a time Tactual, for which the capacitor has an estimated capacitance based on an ageing curve Ccurve, and a time Tlim for which the capacitor will have the forecasted minimum capacitance Clim, with the use of an ageing curve Ccurve of the capacitor and estimating the remaining useful life of the capacitor Tactual−Tlim.

This application discloses a method and computer program product for balancing the DC-side capacitor voltage of an inverter, belonging to the field of inverter technology. The method includes: establishing a spatial vector diagram in the αβ coordinate system based on the inverter topology; dividing the spatial vector diagram into six major sectors, each major sector into 12 minor sectors, or each major sector into 6 minor sectors, with each minor sector including a virtual vector; determining the target sector to which the reference vector to be synthesized belongs; initializing the clamping mode; verifying the initialized clamping mode according to the spatial vector modulation principle to determine the final clamping mode, thus obtaining the target switching sequence; establishing a set of action time equations; obtaining the action time of each vector based on the DC bus capacitor voltage balance constraint or natural balance; and generating a pulse width modulation signal to control the switches. This method can suppress DC-side capacitor voltage fluctuations and reduce inverter switching losses.

The application discloses a life evaluation method, device, equipment and medium of a direct-current bus capacitor, and relates to the technical field of capacitor detection. The life evaluation method comprises the following steps: establishing a simulation model of a motor driving system based on a typical driving cycle of a target electric vehicle, and obtaining a ripple current time sequence of the direct-current bus capacitor in the whole driving cycle. A second-order RC thermal network model of the capacitor is established through finite element thermal simulation fitting, and the ripple current time sequence data is converted into a capacitor hot spot temperature time sequence. Based on a linear cumulative damage theory, the cumulative damage amount of the capacitor under the hot spot temperature time sequence is calculated. An aging feedback mechanism is introduced in the damage accumulation process to update the equivalent series resistance value of the capacitor in real time. A Monte Carlo method is adopted to simulate the manufacturing tolerance of the capacitor through random sampling, a large number of samples are generated and life calculation is performed, and finally, a Weibull distribution is adopted to fit the life data to obtain the reliability index of the capacitor.

The invention discloses a Buck type electronic pre-charging device and method suitable for an energy storage system. The Buck type electronic pre-charging device comprises a Buck constant-current pre-charging circuit, a first switch K1, a second switch K2, a direct-current bus capacitor Cx and a micro-control unit MCU. The Buck constant-current pre-charging circuit comprises a semiconductor switch assembly Q1, a semiconductor switch assembly Q2, an inductor L and an energy storage capacitor Co; the MCU outputs a pulse width modulation (PWM) signal and controls the Q1 to perform switching action at a preset switching frequency and duty ratio; under the switching action of the Q1, the DC bus capacitor Cx is charged through the inductor L, and the MCU realizes constant current control of the charging current by adjusting the duty ratio of the PWM signal in real time. According to the invention, by using the constant current characteristic of the Buck circuit, the pre-charging efficiency is improved, the energy loss is reduced, the charging speed is accelerated, and rapid and efficient pre-charging of the energy storage element is realized.

An electrolysis electrical circuit 14 operatively connected to an AC power source 16 and an electrolysis system 10 is provided, the circuit 14 having: an IGBT rectifier 20 configured to convert the AC power source 16 current to DC and to accommodate fast switching; a DC bus capacitor 30 configured to control the voltage of the downstream DC bus and to power the electrolysis system 10; and a polarization rectifier 40 configured to pre-charge the DC bus capacitor 30 prior to startup of the electrolysis system 10, whereby an inrush current from the AC power source 16 to the DC bus capacitor 30 is reduced.

The application discloses a non-isolated three-level flexible interconnection device and a common-mode current suppression method. The non-isolated three-level flexible interconnection device comprises a controller, a back-to-back power conversion circuit, a first LCL filter, a second LCL filter, a first DC bus capacitor, a second DC bus capacitor, a first common-mode inductor, a second common-mode inductor, a grounding equivalent resistor, a current sensor, a voltage sensor, a first low-voltage area and a second low-voltage area. The back-to-back power conversion circuit controls the size and direction of the power flow transfer between the first low-voltage area and the second low-voltage area by controlling the DC voltage on the DC bus and the size and direction of the output current of the back-to-back power conversion circuit. The controller is used for DC voltage control, power control, common-mode current suppression control and DC midpoint potential balance control, and the DC midpoint potential balance control and the common-mode current suppression control are mutually decoupled. The application realizes the control target of giving consideration to DC voltage balance and common-mode leakage current suppression.