124 results about "Dc capacitor" patented technology

The invention discloses an energy storage type SOP black-start method, system and device based on improved VSG network construction control and a medium, and relates to the field of power grid black-start, and the method comprises the steps: an energy storage type converter MMC carries out the active and reactive control based on an improved VSG network construction control strategy; a non-fault side MMC is controlled to firstly close an isolation circuit breaker and slowly charge a direct-current capacitor, and when the voltage reaches a set threshold value, a current-limiting resistor is quitted; the fault side MMC is started by the same step as the non-fault side MMC; after synchronization is completed, AC circuit breakers between the non-fault side MMC and the feeder load and between the fault side MMC and the feeder load are closed respectively; based on the collected power grid power data, MMC output parameters are adjusted to meet the power grid connection condition, the control mode is switched according to the grid connection state, and the black start process is ended. And by arranging the black start resistor for current-limiting charging and sub-module voltage balance control, the phenomena of overcurrent and voltage unbalance in the black start process are avoided.

A kind of power device parallel type power module and capacitor charging and discharging method, power module includes two or more than pressure type power device, the two or more than pressure type power device adopts the physical form of half bridge group string upper and lower parallel;The half bridge group string of the pressure type power device is connected in parallel by silicon pile composite busbar;Each power module is provided with pneumatic short-circuit switch, in the case of multiple power module series connection, the pneumatic short-circuit switch is connected in series with all DC capacitors, and charging and discharging is carried out through the ground loop of flexible AC transmission equipment AC, DC valve side;The pneumatic short-circuit switch is connected with gas driving pipeline, and the gas driving pipeline is connected with valve-based gas pressurizing device.The power module can effectively improve the capacity of flexible AC transmission equipment, so that it has short-time frequency modulation capacity output, provides technical scheme support for new power system construction, and guarantees system safety and stability;The provided capacitor charging and discharging method can improve maintenance efficiency and enhance product reliability.

The invention provides a transformer DC capacitor state monitoring device and method based on an FPGA, and relates to the technical field of capacitor state monitoring. The device comprises a voltage acquisition module used for synchronously acquiring voltage analog signals at two ends of a DC capacitor in a plurality of MMC modules and performing analog-to-digital conversion; the current acquisition module is used for synchronously acquiring bridge arm current analog signals of a plurality of MMC modules and performing analog-to-digital conversion; the master control FPGA module is respectively connected with the voltage acquisition module and the current acquisition module, and is used for receiving and caching the digitized voltage signal and current signal, respectively calculating a real-time capacitance value of a direct-current capacitor in each MMC module based on a parallel sliding window and a hardware acceleration real-time capacitance value tracking algorithm, and outputting the real-time capacitance value of the direct-current capacitor in each MMC module; the degradation state of each direct-current capacitor is evaluated according to the real-time capacitance value; and the communication module is connected with the master control FPGA module and is used for uploading the degradation state data to an upper computer. According to the method, the real-time performance of monitoring can be remarkably improved while the calculation precision is ensured.

The invention discloses a power module. The power module comprises a direct current busbar, a radiator, an IGBT module I and an IGBT module II, the IGBT module I and the IGBT module II are respectively arranged on a mounting surface I and a mounting surface II of the radiator; the direct-current busbar comprises a direct-current busbar I, a direct-current busbar II, a direct-current busbar III and a direct-current busbar IV; the two ends of a fourth direct-current busbar are connected with the first IGBT module and the second IGBT module respectively, and the middle of the fourth direct-current busbar is connected with the middle of a third direct-current busbar. The two ends of the direct current busbar III are respectively connected with the direct current busbar I and the direct current busbar II; the direct current busbar I and the mounting surface I as well as the direct current busbar II and the mounting surface II are oppositely arranged and parallel to each other; the first direct current capacitor assembly is connected with the first direct current busbar, and the second direct current capacitor assembly is connected with the second direct current busbar. The influence of stray inductance is reduced by optimizing a current path, and the voltage spike at the switching moment is reduced due to the reduction of the stray inductance, so that the switching loss is reduced.

A motor driving device and a home appliance according to one embodiment disclosed herein comprises: a converter for converting input alternating current power into direct current power to output the direct current power; a direct current terminal capacitor for storing the direct current power; an inverter which includes a plurality of upper arm switching elements and lower arm switching elements connected in series, and converts the direct current power from the direct current terminal capacitor into alternating current power to drive a motor; a current detection unit disposed between the direct current terminal capacitor and the inverter; gate drivers for driving the switching elements included in the inverter; bootstrap capacitors which are charged in response to the lower arm switching elements being turned on and supply a driving voltage to the gate drivers of the upper arm switching elements; and a control unit for controlling the inverter on the basis of the current detected by the current detection unit, wherein the control unit first turns some of the plurality of lower arm switching elements on and off and then turns the other lower arm switching elements on and off before driving the motor.

The application provides a pre-charging method and system of a motor train unit traction auxiliary converter, the method comprising: closing an output contactor in the traction auxiliary converter according to a received contactor closing instruction; if no pre-charging instruction is received, judging whether to perform a pre-charging process on a direct current capacitor in the traction auxiliary converter according to a voltage of the direct current capacitor and a preset rated voltage; if yes, obtaining three-phase alternating current voltages and three-phase alternating current of an alternating current port of an auxiliary inverter in the traction auxiliary converter, determining active current feedback values and reactive current feedback values, and generating a pulse signal, and sending the pulse signal to the auxiliary inverter, so that an output voltage of a direct current port of the auxiliary inverter reaches the rated voltage. The application realizes the pre-charging function of the converter without increasing the hardware of the converter, reduces the cost, improves the availability of the converter, reduces the current impact of the switching device and the action frequency, helps to improve the service life and reduce the failure rate.

A distributed ice melting device topological structure suitable for an ultra-high voltage power transmission line comprises a plurality of ice melting sub-modules arranged in a distributed mode, and each ice melting sub-module comprises a single-turn coupling transformer, a metal oxide voltage limiter, a bypass switch, a filter, an H-bridge current converter and a direct-current capacitor. A primary winding of the single-turn coupling transformer is directly formed by split sub-conductors of the ultra-high voltage power transmission line, and a secondary winding of the single-turn coupling transformer is electrically connected with other parts of the ice melting sub-modules, so that the ice melting sub-modules are connected in series on the split sub-conductors of the power transmission line in a distributed manner; the H-bridge current converter is electrically connected with the direct-current capacitor, and the direct-current capacitor provides smooth direct-current voltage for the H-bridge current converter; the filter is connected in series with the H-bridge current converter, the bypass switch is connected in parallel with the H-bridge current converter, and the metal oxide voltage limiter is connected in parallel with the line side output end of the ice melting sub-module; and the ice melting sub-modules adjust the current of the corresponding split sub-conductors by changing the equivalent impedance of the ice melting sub-modules, so that accurate ice melting of the ice-coated split sub-conductors is realized, and the overall current and the transmission power of the power transmission line are kept unchanged. The technical problem to be solved by the invention is to provide the distributed ice melting device topological structure suitable for the ultra-high voltage power transmission line, and the technical problem that the existing ice melting technology cannot realize accurate ice melting and non-power-cut operation on an ice coating section on the ultra-high voltage power transmission line is solved. And normal transmission of the line is affected due to overlarge capacity demand, line overcurrent or incapability of three-phase synchronous ice melting.

The invention discloses a monitoring circuit of a turning thyristor and a monitoring method thereof, and belongs to the technical field of power device control. The monitoring circuit of the turning thyristor is provided with a first driving unit, a second driving unit, a voltage detection unit, a control unit, a first leakage current detection unit and / or a second leakage current detection unit; and detecting the capacitor voltage of the direct current capacitor in real time, identifying a first breakdown result of the first leakage current detection unit and / or a second breakdown result of the second leakage current detection unit, and judging whether the turning thyristor is abnormal breakdown or not by combining the capacitor voltage, the first breakdown result and / or the second breakdown result. Therefore, on-line monitoring of the working state of the turning thyristor is realized, a certain reference significance is provided for analysis of failure reasons of the turning thyristor and improvement of the operation reliability of the modular multilevel converter in high altitude and other scenes, the protection action of the power module is further triggered, the fault range is prevented from being expanded, and reliable operation of direct current transmission is guaranteed.

The application discloses a power assembly and a liquid-cooled converter, the power assembly comprising a capacitor module, a power module and a radiator; the capacitor module comprises DC capacitor banks and a capacitor busbar connected with each other; the power module comprises an input busbar, an output busbar and three single-phase switch tube groups, each single-phase switch tube group comprising a plurality of switch modules and being connected to the input busbar and the output busbar; the input busbar is connected to the connecting part; the output busbar is used for outputting electric energy; and all single-phase switch tube groups in the power module are mounted on the radiator, and the arrangement direction of each switch module in each single-phase switch tube group is parallel to the connecting part. The power assembly can solve the problem of large volume of the existing power assembly.

This application relates to the field of power electronics technology and discloses a method, device, equipment, and storage medium for detecting the aging of DC capacitors in a three-level inverter. The method includes: obtaining a simplified topology model of the three-level inverter; based on the working principle of the three-level inverter, controlling the midpoint current to zero by injecting a zero-sequence voltage into the three-phase reference voltage; under the state of midpoint potential balance, monitoring a first current and a second current using the correlation between capacitor current and capacitance value, calculating the current ratio of the first current and the second current, and deriving the capacitance ratio of the first capacitor and the second capacitor based on the current ratio; and identifying the aging state of the capacitor online based on the capacitance ratio. The device, equipment, and storage medium all correspond to this method. This application achieves online aging identification of capacitors by monitoring the current changes of the upper and lower DC capacitors of a three-level inverter, under the premise that the midpoint potential balance of the three-level inverter is controlled.

A power electronics converter may include: a converter commutation cell having a power circuit and a gate driver circuit, the power circuit including at least one power semiconductor switching element and at least one capacitor, wherein each power semiconductor switching element is embedded in a solid insulating material, wherein each power semiconductor switching element has at least three terminals including a gate terminal, wherein the gate driver circuit is electrically connected to and configured to provide switching signals to the gate terminal of each power semiconductor switching element, wherein a peak rated power output of the power electronics converter is greater than 25 KW, and wherein a total rated capacitance of the power circuit of the converter commutation cell divided by the peak rated power output of the power electronics converter is less than or equal to 5 nF / W.

The invention discloses an inertia frequency support control method and device for an offshore wind power flexible direct output system, and the method comprises the steps: monitoring the frequency of an onshore AC power grid in real time through an onshore converter station, and determining whether the frequency of the onshore AC power grid changes or not; in response to the change of the frequency of the onshore alternating-current power grid, determining a direct-current voltage variable quantity through an offshore converter station, and calculating first capacitance energy provided by a direct-current capacitor based on the direct-current variable quantity; based on the first capacitance energy, calculating a target rotating speed of each wind generator set of the offshore wind plant; and based on the target rotating speed, adjusting the current rotating speed of each wind generator set on the offshore wind plant so as to adjust the inertia frequency supporting capability. According to the invention, energy cooperative control of the offshore wind power plant and the flexible direct-current system can be realized, and the frequency supporting capability of the offshore wind power flexible direct-current delivery system to an onshore alternating-current power grid is improved.

The present invention relates to a control device for a cooling and heating system. The control device for a cooling and heating system according to one embodiment of the present invention is a control device for controlling a motor of an electric compressor for cooling and a positive temperature coefficient (PTC) heater for heating, and for performing control in response to removal of a power supply unit. The control device comprises: a DC capacitor for storing DC power inputted from the power supply unit; a power conversion unit having a plurality of switching elements and configured to convert the DC power stored in the DC capacitor into AC power on the basis of a switching operation to output the AC power to the motor; a PTC switching unit connected in series with the PTC heater to switch application of the DC power of the DC capacitor to the PTC heater; and a control unit positioned between the power supply unit and the DC capacitor to determine an active state of the power supply unit.

The application provides a multi-output DC-DC converter based on shared DC capacitor, comprising a power conversion unit, an energy sharing regulation unit and an output unit; the power conversion unit is arranged between a power supply end and the output unit, and comprises a plurality of flying capacitors and a plurality of power switching tubes, thereby forming a flying capacitor switching network; the energy sharing regulation unit is connected with the power conversion unit, and comprises a DC capacitor and a plurality of power switching tubes, thereby forming a DC capacitor switching network; the output unit comprises a plurality of inductors and a plurality of output capacitors, thereby forming an inductor-capacitor output network, and the output unit has a plurality of output ends; the charging and discharging of the flying capacitor and the charging and discharging of the inductor are controlled by controlling the on-off of the power switching tubes in the power conversion unit and the energy sharing regulation unit, so that the output ends provide energy for loads, the DC capacitor is charged and discharged to store energy and provide energy for the output ends, and independent regulation of the output ends is realized.

A vehicle is provided that includes a traction motor. The traction motor includes a direct current capacitor (DC capacitor) and a printed power circuit board (power PCB) that converts the direct current power (DC power) received by the DC capacitor into alternating current power (AC power). The traction motor also includes a stator with windings. The traction motor further includes a first phase connection, a second phase connection, and a third phase connection arranged between the power PCB or power module and the stator windings. The first, second, and third phase connections provide an electrical connection between the power PCB or power module and the stator windings and are arranged in a triangular configuration to supply AC power to the stator windings.The traction motor also includes a triangular AC choke that encloses the first phase connection, the second phase connection and the third phase connection in the triangular configuration.

The invention discloses a transient stability margin evaluation method for a grid-forming type permanent magnet wind power system considering current saturation, and the method comprises the steps: obtaining an implicit expression of a current-limiting trigger angle through the instantaneous variation of the active power transmission limit of the system caused by the triggering of a current limiter, and solving the current-limiting trigger angle; when a three-phase symmetric short-circuit fault occurs in a power grid, a transient stability margin evaluation index gamma of the grid-forming type permanent magnet direct-drive wind power system considering current saturation is defined, the gamma value is calculated in real time, and the transient stability and the transient stability margin of the grid-forming type permanent magnet direct-drive wind power system are judged and evaluated according to the gamma value during the three-phase symmetric short-circuit fault of the power grid. According to the method, the transient stability margin and influence factors of the grid construction type permanent magnet direct-driven wind power system adopting direct current capacitance synchronization during the three-phase symmetric short-circuit fault period of the power grid can be reflected, whether the transient synchronization of the system is stable or not under the current saturation working condition can be visually judged, and the power angle instability risk of the new energy grid-connected system can be reduced.

The invention relates to the technical field of energy storage unit control, and discloses a method, a device and equipment for controlling the wide short-circuit ratio of a full-power pumped storage unit, and a medium. The method comprises the following steps of: controlling a grid-side converter by using a wide short-circuit ratio network construction type control strategy; wherein the control strategy of the wide short-circuit ratio network construction type comprises the following steps: tracking a reference voltage obtained according to a first output voltage output by a network-side current inner loop and a network-side three-phase current transmitted by a network-side converter by using a voltage and current double closed-loop control strategy, and obtaining a second output voltage of a network-side current loop; generating a first switching signal according to grid-side phase information of operation of the grid-side converter and the second output voltage so as to drive the grid-side converter; acquiring voltages at two ends of the direct-current capacitor to obtain a capacitor voltage actual value; and generating a second switching signal according to the capacitor voltage actual value and the capacitor voltage reference value so as to drive the machine-side converter. Therefore, the stability of the full-power pumped storage unit is improved.

The invention relates to a model selection method, system and device for a DC capacitor of a photovoltaic inverter and a medium, and the method comprises the steps: obtaining a loop stray inductance value of a DC-DC loop in the photovoltaic inverter through calculation; based on the real working environment parameters of the photovoltaic inverter, calculating to obtain an impulse voltage correction value of a direct current capacitor in the photovoltaic inverter; on the basis of the impact voltage correction value and the loop stray inductance value, the impact voltage of the direct-current capacitor is obtained through calculation; and calculating an output combined voltage of a programmable power supply in the durability test platform based on the impulse voltage so as to carry out a durability test on the direct-current capacitor to obtain the direct-current capacitor meeting a preset safety requirement. According to the method and the device, the real working environment parameters are used for correction on the impact voltage simulation calculation of the direct current capacitor, so that the endurance test is carried out to obtain the direct current capacitor meeting the requirement, the safe operation level of the inverter in different working environments is effectively improved, and the problem of how to select the type of the direct current capacitor of the photovoltaic inverter is solved.

The invention discloses a frequency cooperative control system, method and device for a flexible interconnection low-voltage power distribution network and a medium, and belongs to the technical field of flexible interconnection power distribution networks, and the method comprises the steps: building an equivalent circuit model of the DC side of a multi-end feed-in flexible hub switch, calculating the impedance analytical expression of each converter and DC capacitor, and calculating the impedance analytical expression of each converter and DC capacitor; obtaining a quantitative index for measuring the stability margin of the direct current side of the system; if not more than 0, positioning a direct current side unstable link and optimizing control parameters of the direct current side unstable link; if gt; and if yes, completing the parameter design, and applying the control parameter to the frequency cooperative control of the flexible interconnection low-voltage power distribution network. According to the method, the internal interaction stability of the device is evaluated by constructing quantitative indexes, weak links of the stability can be positioned, control parameters are optimized in a targeted manner, and the overall operation stability is effectively improved; meanwhile, when frequency deviation occurs in the power distribution network on one side, power absorption or release of the internal energy storage device can be regulated and controlled on the premise that normal operation of the power distribution network on the other side is not interfered.

The application discloses a pumped storage full-power frequency converter power unit variable frequency control method and device, N power units are cascaded at an AC end to form a test valve, and M power units are cascaded at the AC end to form a test valve; the method is used for controlling the test valve to output several AC frequency target values, and the method comprises the following steps: pre-charging DC capacitors in the test valve and the test valve to target values; determining corresponding output current / power target values according to the AC frequency target values to be output; controlling the turn-on and turn-off time of the turn-off semiconductor of each power unit in the test valve and the test valve, so that the actual output current / power of the test valve is the output current / power target value, and the actual output frequency of the test valve is the AC frequency target value. The application can simulate the continuous speed regulation operation condition of the pumped storage full-power frequency converter power unit on the pumped storage unit.

The invention provides a multi-output direct current-direct current converter based on a shared direct current capacitor. The multi-output direct current-direct current converter comprises a power conversion unit, an energy sharing adjusting unit and an output unit, the power conversion unit is arranged between the power supply end and the output unit, the power conversion unit comprises a plurality of flying capacitors and a plurality of power switch tubes, and a flying capacitor switch network is formed; the energy sharing adjusting unit is connected with the power conversion unit and comprises a direct-current capacitor and a plurality of power switch tubes to form a direct-current capacitor switch network; the output unit comprises a plurality of inductors and a plurality of output capacitors to form an inductor-capacitor output network, and the output unit is provided with a plurality of output ends; charging and discharging of a flying capacitor and magnetizing and demagnetizing of an inductor are controlled by controlling on-off of power switch tubes in the power conversion unit and the energy sharing adjusting unit, so that each output end provides energy for a load, energy is stored and provided for each output end through charging and discharging of a direct current capacitor, and independent adjustment of each output end is achieved.

The invention provides an evaporation method of a metallized film for a flexible capacitor, and relates to the technical field of evaporation, and the evaporation method comprises the following steps: S1, pretreatment: carrying out surface treatment on a polypropylene film base material through a pretreatment device of a film plating machine to enable the surface of the polypropylene film base material to reach a to-be-evaporated state; s2, the evaporation area is limited, specifically, the pretreated polypropylene film passes through the lower portion of a specially-made oil screen system, and the oil screen system is provided with a specially-made oil plate which is used for limiting the evaporation area with the preset shape and size on the film. According to the invention, a complete process chain of pretreatment device cleaning and activation, successive collaborative patterning and sheet resistance control of a special oil screen system and a special zinc plate mold, matched evaporation of an electronic gun system, surface stabilization of a post-treatment system, and undamaged rolling of a flattening and tension system is adopted; and the metallized polypropylene film with high-precision patterns, super-uniform sheet resistance, strong adhesive force and no-defect film surface is systematically prepared, so that the stability of a system and the quality of electric energy are comprehensively improved.

To prevent such a problem that a predetermined volts alternating current required for system interconnection cannot be output from an SST when operation is continued in the case where a part of cells fails.SOLUTION: A plurality of cells each including an AC-DC converter ACDC, a primary-side DC capacitor C1, an insulated DC-DC converter DCDC, and a secondary-side DC capacitor C2 are provided per phase. A plurality of DC systems to which a plurality of secondary side DC capacitors C2 are connected in parallel are provided, and voltages of the plurality of DC systems are supplied to a load or a power source. When a cell fails, the control unit of the AC / DC converter ACDC increases the output voltage on the AC system side of the cell connected to the same DC system as the failed cell, and decreases the output voltage on the AC system side of the cell connected to the other DC system. The third harmonic is superimposed on the AC output voltage of the cell connected to the same DC system as the failed cell, and the third harmonic in the opposite direction is superimposed on the AC output voltage of the cell connected to the DC system different from the failed cell.SELECTED DRAWING: Figure 1

The invention relates to the technical field of anti-interference receiving, and discloses a tunable high-temperature superconducting amplitude limiter based on voltage regulation. Comprising a radio-frequency signal input end P1, a first impedance conversion node assembly, a superconducting amplitude limiting node L4, a direct-current bias regulation and control circuit for introducing bias current to the superconducting amplitude limiting node L4, a second impedance conversion node assembly and a radio-frequency signal output end P2 which are electrically connected in sequence, the first impedance conversion node assembly and the second impedance conversion node assembly are the same in structure, and each of the first impedance conversion node assembly and the second impedance conversion node assembly comprises a superconducting microstrip transmission line, a blocking capacitor and an impedance conversion node, on the premise that geometric structure parameters of the high-temperature superconducting amplitude limiting section are not changed, the working current density of the high-temperature superconducting amplitude limiting section can be changed within the range close to or away from the critical current density of the superconducting material by adjusting the magnitude of the bias current, and therefore tuning of the amplitude limiting threshold value and the power bearing capacity of the amplitude limiter is achieved.

The present invention relates to an inverter of a cooling and heating system. The inverter of a cooling and heating system, according to one embodiment of the present invention, controls each of a motor of an electric compressor for cooling and a positive temperature coefficient (PTC) heater for heating, and comprises: a power source unit for supplying a power source; a DC capacitor for storing a direct current power source that is input from the power source unit; a power conversion unit having a plurality of switching elements, and converting, on the basis of the switching operations of respective switching elements, the direct current power source stored in the DC capacitor into an alternating current power source so as to output same to a motor; a PTC switching unit connected to the PTC heater in series so as to switch whether the direct current power source of the DC capacitor is applied to the PTC heater; a converter for converting each of a signal of one end of the DC capacitor, a signal of the power conversion unit, and a signal of one end of the PTC heater into a digital signal; and a digital isolator which converts the digital signal into an output signal to transmit same to a control unit, and which insulates the converter and the control unit.

This invention discloses an active disturbance rejection energy feedback control method and system for a variable frequency drive motor, belonging to the field of motor drive control technology. The method includes: employing a virtual synchronous motor control strategy for the grid-side rectifier of the back-to-back inverter to provide virtual inertia and damping to the power grid; employing vector control for the motor-side inverter; establishing a small-signal model of the system; and adaptively tuning the virtual inertia and damping parameters based on the model response characteristics and DC voltage constraints to achieve active disturbance rejection energy feedback during regenerative braking. The system includes: a back-to-back inverter, a grid-side rectifier controller, a motor-side inverter controller, and a parameter tuning module, which work together to implement the above method. This invention effectively suppresses the impact of feedback power on the power grid, fully utilizes the buffering capacity of the DC capacitor, and achieves efficient energy feedback while ensuring DC voltage stability, thereby improving the overall energy efficiency and operational safety of the system.

The invention relates to an energy storage converter harmonic wave and double frequency suppression method. By sampling the inductive current output by the DC / AC converter, dead time compensation is carried out, low-order harmonics in the output voltage can be reduced, and the quality of output electric energy is improved. Band elimination filtering is performed on voltage sampling feedback of the DC / DC converter, so that the output DC capacitor of the DC / DC converter bears frequency doubling power, the power fluctuation of an energy storage element is reduced, the service life of the energy storage element can be prolonged, the loss of the energy storage converter is reduced, and the performance and the power density of the energy storage converter are improved.

The application discloses a double-fed fan subsynchronous oscillation additional damping controller based on capacitor current compensation and relates to the field of novel power system stability analysis and control; solves the problems that the existing controller is relatively complex in determining control parameters, lacks universality and operation parameters cannot be modified at will; comprises a small signal model structure based on double-fed induction fan and weak power grid grid connection, and a general phase lead compensation link controller; phase compensation controller parameters are determined through double-fed induction fan voltage and current frequency response curves; the original system control structure can be not changed, the original control parameters of the system do not need to be adjusted, direct DC current signals are obtained from the DC capacitor part of the double-fed fan, control currents are injected in the form of controlled current sources, the rotor side control and the grid side control are decoupled, and the subsynchronous oscillation phenomenon caused by the interaction between the double-fed fan phase-locked loop and the weak power grid is suppressed.

The application provides a vehicle-mounted charging system and a control method thereof. The vehicle-mounted charging system comprises: a converter, one side of which is capable of being coupled with an external AC power source outside a vehicle, and the other side of which is coupled with a power battery of the vehicle; an inverter, which is coupled between the power battery of the vehicle and a motor, comprises a plurality of bridge arms and a DC capacitor, each bridge arm comprises an upper bridge arm switch and a lower bridge arm switch, and the DC capacitor is connected across positive and negative bus bars; a group of on-off switches, which comprises a first on-off switch and a second on-off switch, the first on-off switch is arranged on the positive bus bar, and the second on-off switch is connected with a middle node between the upper bridge arm switch and the lower bridge arm switch of one bridge arm of the plurality of bridge arms; and a controller, which is configured to control the operation of the vehicle-mounted charging system by controlling the combined state of each on-off switch and the upper and lower bridge arm switches of another one or another two bridge arms of the plurality of bridge arms which are not connected with the second on-off switch.

The invention discloses a grid-connected converter direct-current side midpoint potential balance structure, and the structure comprises a direct-current circuit structure which comprises a direct-current positive electrode, a midpoint potential and a direct-current negative electrode; the multi-winding transformer is provided with a primary side winding and a secondary side winding, and the primary side winding is electrically connected to the direct current circuit structure between the direct current positive electrode and the midpoint potential and the direct current circuit structure between the midpoint potential and the direct current negative electrode through a primary side H-bridge inversion module; and the voltage source type inverter is electrically connected to the secondary side winding, so that an energy interaction channel is formed between the voltage source type inverter and the multi-winding transformer, and when the unbalanced magnetomotive force is generated, the secondary side winding generates a compensation current for the neutral point potential through the energy interaction channel. The primary side of the multi-winding transformer is connected with two capacitors on the direct current side, the secondary side of the multi-winding transformer is connected with the voltage source type inverter, current compensation is carried out on the offset neutral-point potential, the neutral-point potential can be automatically corrected, the development difficulty and delay of a balance algorithm are eliminated, and the adjusting speed and the balance capacity are improved.