37results about How to "No overcurrent" patented technology

The invention discloses a mixed bipolar DC transmission system. The system comprises a rectification converter station and an inversion converter station which are connected through a DC transmission line, wherein the rectification converter station is formed by two thyristor converters through serial connection, and the serial connection node is grounded; and the inversion converter station is formed by two modular multilevel converters (MMCs) through serial connection, the serial connection node is grounded, and positive and negative ends after serial connection are connected with one-way connection power devices. The system has the advantages of low cost and loss, high reliability and the like of the existing thyristor converter, flexible control of the MMCs, low harmonic, active-reactive power decoupling control, low dependence on an alternating current system and the like; and the system is divided into positive and negative poles, so that operating reliability is strengthened, and the power devices provided with the one-way connection capacity and additionally arranged at outlets of inverters can effectively handle DC faults. The system is suitable for occasions such as high-power long-distance high-voltage DC transmission and island current delivery, provided with broad development space, and worthy of being popularized vigorously.

The invention discloses a closed loop starting method for a resonant converter. The resonant converter comprises a bridge circuit, a resonant circuit, a transformer, a rectifier circuit, a filter circuit, an input detection circuit, a driving circuit, a peak detection circuit, an output detection circuit and a digital processor, wherein the bridge circuit, the resonant circuit, the transformer, the rectifier circuit and the filter circuit are sequentially connected in series. The input detection circuit is connected to the input end of a resonant transformation device to detect the input voltage and send the input voltage to the digital processor. The driving circuit is connected to the digital processor and converts a PWM signal into the driving level so as to drive the bridge circuit. The peak detection circuit is connected with the resonant circuit, detects the resonant current peak and sends the resonant current peak to the digital processor. The output detection circuit detects the output voltage and the output current and sends the output voltage and the output current to the digital processor. According to the closed loop starting method for the resonant converter, due to the fact that the peak detection circuit detects the resonant current peak, implementation is easy. Closed loop control is conducted on the resonant current peak in the starting process, control is easy, it is ensured that the overcurrent of the resonant converter cannot occur in the starting process, and the starting time is made optimal.

The invention discloses a low-voltage ride-through control method for a grid-connected inverter. Whether a power grid works properly can be judged through a dropping state judgment device, so the method has the advantage of being fast in power grid judgment. In specific configuration, the method includes the steps of controlling a given current calculation module to calculate given current target values of the power grid in a normal working state and in a dropping state, and controlling a feedforward weight calculation module to distribute reasonable specific gravity of different voltage feedforward quantities according to the voltage state of the power grid agine. Consequently, current impact at the instant of voltage drop of the power grid can be restrained, and the recovery rate of the current waveform after voltage drop of the power grid can be increased so that the balance of three-phase current output by the inverter during voltage drop of the power grid can be maintained. Thus, it is guaranteed that the grid-connected inverter is in a fault ride-through state and accords with national standard inverter grid-connection requirements.

The invention discloses an LED light-emitting lamp filament and an LED bulb adopting the same. The LED light-emitting lamp filament comprises a strip-shaped substrate and multiple LED chips arranged on the strip-shaped substrate. The two ends of the strip-shaped substrate are each provided with a metal strip-shaped electrode. The multiple LED chips are connected in series to form an LED light source. Multiple electronic devices having one of the conductive function, the current-limiting function and the protection function are arranged at the position, close to one of the ends, on the strip-shaped substrate or the position, close to each of the ends, on the strip-shaped substrate. The metal strip-shaped electrodes, the electronic devices and the LED light source are connected through a wire. The periphery of the strip-shaped substrate, the periphery of the LED light source, the periphery of each electronic device and the periphery of the connection position between the strip-shaped substrate and each metal strip-shaped electrode are coated with fluorescent rubber. The LED light-emitting lamp filament and the LED bulb adopting the same have the beneficial effects that according to different properties of the electronic devices, the connection wire of the LED light source and the metal strip-shaped electrodes can be prevented from rupture; or a current of the LED light-emitting lamp filament can be prevented from overcurrent; or the LED light-emitting lamp filament can be free from influence of overvoltage and overcurrent; or when the LED light-emitting lamp filament is overheated, the heat emitting phenomenon is reduced.

The invention relates to a combined type sensor, which belongs to the field of electric power measurements. The combined type sensor comprises a shell, and is characterized in that a V / I / v voltage sampling loop and an I / i current sampling loop are arranged on a measured high-voltage load conducting wire in the shell, and an output end of the V / I / v voltage sampling loop and an output end of the I / icurrent sampling loop are connected with a current interface and a voltage interface of an output interface of the shell respectively. The combined type sensor can acquire supplied weak current signals, supplies the signals to a measuring instrument of milliampere or microampere standard current signals and millivolts or microvolt standard voltage signals to perform measurement, can acquire the signals accurately, reduce the consumption, save the cost and prevent electric larceny, is save and stable, and is suitable for measuring the electric quantity of a high-voltage side.

A motor controlling device of electrical fishing line reel capable of preventing the motor loading weighting to prevent the motor being burnout when controlling the speed of the motor at multiple stages, comprising a brake unit , a winding reel sensor detecting the rotating speed of the winding reel; a current detecting portion for detecting the load of the winding reel by current value; an adjusting rod; the rotating speed of the winding reel is divided into high and low grades; the adjusting rod sets the speed upper limit value of each grade; when satisfying the first condition, for the load detected by the load detecting portion, if the motor current maintains time t5 by state of above the first current value less than the maximum current value, the fishing line reel controlling portion degrades the speed of the motor to at least a grade and setting the speed corresponding to the speed upper limit value below the grade as the target speed; comparing the first load setting the target speed and trhe second load after t5, if the second load is more than the second load in set quantity, setting the target speed as a lower speed upper limit value; when satisfying the first speed, the speed of the winding reel is accordant with the target speed.

The invention discloses a method for estimating the available discharge of a battery and a method for estimating the available feedback power of the battery and belongs to the field of automobile batteries. The method for estimating the available discharge power of the battery includes the following steps that: an SOC-continuous discharge power curve and an SOC-peak discharge power curve are collected; an SOC-battery initial available discharge energy curve is established; the discharge recovery energy and discharge warning energy of the battery are calculated; the maximum available dischargeenergy of the battery is calculated; and the available discharge power of the battery is estimated. The method for estimating the available feedback power of the battery includes the following steps that: an SOC-continuous feedback power curve and an SOC-peak feedback power curve are collected; an SOC-battery initial available feedback energy curve is established; the feedback recovery energy andfeedback warning energy of the battery are calculated; the maximum available feedback energy FBCapLeft of the battery is calculated; and the available feedback power of the battery can be estimated. With the method for estimating the available discharge of the battery and the method for estimating the available feedback power of the battery of the invention adopted, the potential of the battery can be given to full play with the safety and service life of the battery ensured; available power can be provided; user experience can be effectively improved; and the recovery efficiency of braking energy can be improved.

The invention provides a direct-current converter station and a control method and system thereof. The control method of the direct-current converter station comprises: controlling a receiving end converter station by adopting an active-reactive control method; adding an input power regulation module at the input end of an active-reactive power control power loop, and connecting the input power regulation module with an active-reactive power control power loop; and adjusting, by the input power adjusting module, an input power instruction of active-reactive control according to the voltage ofthe receiving end power grid and the voltage of the receiving end direct-current bus. By utilizing the method, reactive power can be continuously provided for the power grid when the voltage of the receiving-end power grid drops, an over-current phenomenon does not occur in the converter station, the system can stably operate after fault recovery, the direct-current bus voltage can be stabilized when the voltage of the sending-end power grid drops, and the system can stably operate after fault recovery.

The invention discloses a control circuit for a power generator for a hazardous article transport vehicle. The control circuit comprises a power generator, a storage battery connected with the outer part of the power generator and a vehicle electrical appliance load; the power generator comprises an adjustor, a magnet exciting coil and a three-phase rectifier bridge, wherein the output end of the three-phase rectifier bridge is connected with the storage battery and the vehicle electrical appliance load; the input end of the three-phase rectifier bridge is simultaneously connected with the anode of a rectifying diode set and a star-shaped stator coil; the negative electrode of the magnet exciting coil is connected with the adjustor; the other end of the adjustor is connected with a ground wire; the positive electrode of the magnet exciting coil is connected with a piece of dropping equipment; the other end of the dropping equipment is connected with a power master switch by a charging indicator lamp; the dropping equipment comprises a relay and a first external joint; the cathode of the rectifying diode set and the regulator are connected with the first external joint. The control circuit can avoid generating overvoltage and over-current, and is also applicable to the power generator on the hazardous article transport vehicle. Moreover, the control circuit is low in production cost, and is easy to maintain and change.

The invention provides a DC voltage transformation subunit and a DC transformer comprising the DC voltage transformation subunit. The DC voltage transformation subunit comprises a fault isolation voltage equalization module and a DC / DC converter, wherein a high-voltage side of the fault isolation voltage equalization module is connected with a high-voltage direct-current bus, a low-voltage side ofthe DC / DC converter is connected with a low-voltage DC bus, the mass and the occupied area are small, cost is low, a DC transformer of the DC voltage transformation subunit comprises a plurality of DC voltage transformation subunits. The DC voltage transformation subunit is advantaged in that high-voltage sides of a plurality of DC voltage transformation subunits are connected in series, withstand voltage class requirements are met, low-voltage sides of the multiple DC voltage transformation subunits are connected in parallel, the high-power requirement is met, the number of layers of the DCvoltage transformation subunits is greatly reduced, the occupied area is reduced, cost is saved, different application scenes of one-way power flowing and two-way power flowing can be met, and automatic isolation and crossing of faults on the high-voltage side can be achieved.

The invention discloses a static off-line parameter identification method of a permanent magnet synchronous motor. The method comprises the steps that firstly, high-frequency rotation voltage with the angular frequency being omegac and the amplitude being urot is input into a stator winding of the permanent magnet synchronous motor, and the amplitude urot of the input voltage is gradually adjusted until the appropriate amplitude of the input high-frequency rotation voltage is found; secondly, the appropriate high-frequency rotation voltage obtained in the first step is input into the stator winding of the permanent magnet synchronous motor for 1000ms, and rotor magnetic pole initial position identification, direct-axis inductance identification and quadrature axis inductance identification are conducted; thirdly, stator resistance is identified through an automatic-adaption two-point type voltammetry in the direction of a rotor magnetic pole obtained through identification in the second step. By the adoption of the static off-line parameter identification method of the permanent magnet synchronous motor, the influence of saturation of a magnetic circuit of a rotor on inductance identification is eliminated, the influence of system non-linear factors on the resistance identification is eliminated, the identification precision is high, the identification time is short, and the rotor can be kept static.

The invention discloses a metering calibration method of a lightning protection element tester. The method comprises the following steps: S1, a lightning protection element tester tests a piezoresistor and other components, wherein the output DC voltage range is 0-2000 V in operation, and the DC current range is 0-1000 [mu]A; S2, a voltage terminal distinguishes high-end output from low-end output; S3, a direct-current high-resistance voltage divider or a digital high-voltage meter is connected to the high end and the low end in parallel, and voltage parameters are measured; and S4, the current value of the lightning protection original tester is measured by using a high-voltage high-resistance box and a digital multimeter. According to the invention, aiming at the characteristic that calibrated equipment is a voltage source, a high-resistance voltage divider or a digital high-voltage meter is used for measuring voltage, so that the influence of the internal resistance of a measuring instrument on a voltage measurement value is avoided; and a high-voltage high-resistance resistor is used for adjusting the current of a measurement loop, so that the state of the lightning protectionelement tester in the actual use process can be simulated, and the whole measurement loop can be protected from generating overcurrent.

The invention discloses a pre-charging method for a full-bridge type MMC. The pre-charging method is divided into an uncontrolled charging phase and a controllable charging phase. In the uncontrolledcharging phase, all sub-modules are in a locked state, and the phenomenon that no overcurrent occurs in the charging process can be ensured through a series current limiting resistor; and in the controllable charging phase, a full-bridge sub-module trigger system is used to charge and withdraw the sub-modules of each bridge arm in a grouping mode, so that capacitors of the sub-modules are chargedto the rated voltage to complete a pre-charging process. According to the scheme of the invention, the phenomenon that the full-bridge type MMC takes power from an alternating current system in the pre-charging phase can be ensured, and meanwhile, a direct current line can be prevented from bearing a huge voltage change ratio, and the voltage of each sub-module can be raised to a rated voltage value of the sub-modules after the pre-charging process is completed.

The invention relates to a battery pack structure. The battery pack structure comprises a support (1), a protection sleeve (2) and buffers (3), wherein the buffers are arranged around the support, the protection sleeve wraps the support and the buffers, a battery (4), an installation groove (5), a protection plate (6) and a connector (7) are arranged on the support, the battery is placed in the installation groove, the connector is connected with the protection plate, and an overcurrent protector (8) and a temperature sensor (9) are arranged on the protection plate and both are connected with a positive electrode or a negative electrode of the battery. By the battery pack structure, the safety of a battery pack can be ensured, and an overcurrent phenomenon is prevented; moreover, compared with other battery packs with same capacity, the battery pack structure has the advantage of small size and is convenient to use; and meanwhile, the performance the battery pack is enabled not to be damaged during collision.

A high-reliability isolation drive circuit suitable for wide duty cycle for spacecrafts relates to the field of spacecraft high-voltage power system protection and design. The isolation drive circuitincludes a drive generation circuit, a drive enhancement circuit, a drive isolation module, a rectifier module and an MOS tube parallel circuit. The drive generation circuit generates two pulse drivecurrents. The drive enhancement circuit enhances the two pulse drive currents, and provides a drive current required for switching on MOS tubes. The drive isolation module isolates the drive circuit from a spacecraft power supply and expands the duty cycle. The rectifier module provides a path for the switch-on voltage and switch-off current for driving the MOS tubes. The MOS tube parallel circuitexpands the duty cycle. The problems of burnout caused by the requirement of the high-voltage spacecraft system that the MOS tubes should be out of control in the process of abnormal power failure, the requirement for duty cycle of 0-98% and serious EMC interference are solved, and the working reliability of the spacecraft power control equipment is improved.

The invention discloses a single-damper single-resistor star-connection non-vibration brake frequency conversion device which comprises a frequency converter. The frequency converter comprises a power circuit, a rectifying circuit, an inverter circuit, a main control circuit, a driving circuit, a voltage sampling circuit and a current sampling circuit. The single-damper single-resistor star-connection non-vibration brake frequency conversion device further comprises a damping circuit and an electromagnetic valve. The three output ends of the damping circuit are connected with the electromagnetic valve in series and connected with the three output ends of the inverter circuit correspondingly, and the control input end of the electromagnetic valve is connected with the damping control signal output end of the main control circuit. The damping circuit comprises three resistors, one end of each resistor is connected with one end of another resistor, and the other ends of the three resistors respectively serve as the three output ends of the damping circuit. According to the single-damper single-resistor star-connection non-vibration brake frequency conversion device, the resistors in the damping circuit are used for consuming energy at the output ends, namely the load ends, of the inverter circuit so as to achieve the braking purpose, and no vibration, no noise, no overvoltage, no overcurrent and no temperature rise exists in the braking process. The single-damper single-resistor star-connection non-vibration brake frequency conversion device is an upgraded product of a traditional frequency converter.

The invention provides a motor control method and circuit for stable operation of an AC motor in a full frequency band, the low-speed and high-speed control switching is smooth, the stable range is widened, the speed regulation range is wide, and the application is wide. The method includes the steps of performing deviation processing on a given current Idref generated according to a set frequencyand a feedback current Idfed generated by collecting a current of an AC motor; performing PID control on the obtained deviation to generate an initial given direct-axis voltage; performing amplitudelimiting on the initial given direct-axis voltage according to an operating direction of the AC motor to obtain a given direct-axis voltage Udref; obtaining the corresponding set rotational speed according to the set frequency and obtaining a given quadrature-axis voltage Uqref from the set rotational speed; and synthesizing the given direct-axis voltage Udref with the quadrature-axis voltage Uqref to output the value and angle of the control voltage of the AC motor.

A motor controlling device of electrical fishing line reel capable of preventing the motor loading weighting to prevent the motor being burnout when controlling the speed of the motor at multiple stages, comprising a brake unit , a winding reel sensor detecting the rotating speed of the winding reel; a current detecting portion for detecting the load of the winding reel by current value; an adjusting rod; the rotating speed of the winding reel is divided into high and low grades; the adjusting rod sets the speed upper limit value of each grade; when satisfying the first condition, for the load detected by the load detecting portion, if the motor current maintains time t5 by state of above the first current value less than the maximum current value, the fishing line reel controlling portion degrades the speed of the motor to at least a grade and setting the speed corresponding to the speed upper limit value below the grade as the target speed; comparing the first load setting the target speed and trhe second load after t5, if the second load is more than the second load in set quantity, setting the target speed as a lower speed upper limit value; when satisfying the first speed, the speed of the winding reel is accordant with the target speed.

The present invention relates to a blade tool (1) suitable for use in a kitchen appliance, the blade tool (1) comprising a first arm (2) and a second arm (3) each forming a blade for processing food a shaft (4) supporting the first arm (2) and the second arm (3), wherein the shaft (4) has a coupling (5) for engaging with a rotary drive shaft of the kitchen appliance. In the blade tool (1) according to the present invention, a sharp cutting edge (6) is formed at a leading edge (7a) of the first arm (2) with respect to a first rotation direction and a paddle (8) is formed at a leading edge (7b) of the second arm (3) with respect to a second rotation direction opposite to the first rotation direction. The present invention also relates to a kitchen appliance for processing food, comprising a control unit for controlling rotation of a blade tool (1).

The invention discloses a method and system for controlling energy of a two-motor controller with a boosting apparatus. The method comprises the following steps: calculating surplus power by virtue of current parameters, ensuring the output power of one motor system of the two-motor controller in priority according to a current working mode and state, feeding back an allowable output torque of the motor system in real time, and ensuring a first motor system and a second motor system not to have over-current phenomenon in an application process. A maximum demand of an entire car can be satisfied, and the maximum output performance of the two-motor controller is played. In addition, current value is adopted for calculation, so that time delay is reduced, and the over-current fault of the two-motor system or the risk of damaging the two-motor system are reduced.

A control circuit, a control method and a harmonic converter are disclosed. A start control signal correspondingly changing with the duration of the soft start process is generated as a loop variable,the loop variable shows different change trends when the resonant current intensity is in different intervals, and thus, a resonant circuit can be started by controlling the converter. The change speed of the soft start loop variable is dynamically adjusted according to the actual current of the resonant circuit, so that the resonant circuit can be started quickly without causing over-current. Atthe same time, there is no need to make corresponding adjustment according to the application example, and the design process of the resonant circuit is simplified.

The invention discloses a low-voltage ride-through control method for a grid-connected inverter. Whether a power grid works properly can be judged through a dropping state judgment device, so the method has the advantage of being fast in power grid judgment. In specific configuration, the method includes the steps of controlling a given current calculation module to calculate given current target values of the power grid in a normal working state and in a dropping state, and controlling a feedforward weight calculation module to distribute reasonable specific gravity of different voltage feedforward quantities according to the voltage state of the power grid agine. Consequently, current impact at the instant of voltage drop of the power grid can be restrained, and the recovery rate of the current waveform after voltage drop of the power grid can be increased so that the balance of three-phase current output by the inverter during voltage drop of the power grid can be maintained. Thus, it is guaranteed that the grid-connected inverter is in a fault ride-through state and accords with national standard inverter grid-connection requirements.

The invention discloses a closed loop starting method for a resonant converter. The resonant converter comprises a bridge circuit, a resonant circuit, a transformer, a rectifier circuit, a filter circuit, an input detection circuit, a driving circuit, a peak detection circuit, an output detection circuit and a digital processor, wherein the bridge circuit, the resonant circuit, the transformer, the rectifier circuit and the filter circuit are sequentially connected in series. The input detection circuit is connected to the input end of a resonant transformation device to detect the input voltage and send the input voltage to the digital processor. The driving circuit is connected to the digital processor and converts a PWM signal into the driving level so as to drive the bridge circuit. The peak detection circuit is connected with the resonant circuit, detects the resonant current peak and sends the resonant current peak to the digital processor. The output detection circuit detects the output voltage and the output current and sends the output voltage and the output current to the digital processor. According to the closed loop starting method for the resonant converter, due to the fact that the peak detection circuit detects the resonant current peak, implementation is easy. Closed loop control is conducted on the resonant current peak in the starting process, control is easy, it is ensured that the overcurrent of the resonant converter cannot occur in the starting process, and the starting time is made optimal.

The high-reliability DC / DC switching power supply composed of discrete parts of the present invention is composed of a power main loop and a control loop. This switching power supply has the characteristics of high isolation, good stability, small size, light weight, high conversion efficiency, etc., and this switching power supply has no protection measures such as overcurrent and overvoltage, which is especially suitable for Shangtian products.

The present invention provides a DC converter station and its control method and control system. The DC converter station control method includes controlling the sending-end converter station by using a constant DC voltage control method; controlling the receiving-end converter station by using an active-reactive power control method. flow station; wherein, wherein, the step of controlling the receiving end converter station using the active-reactive power control method includes: adding an input power adjustment module at the input end of the power loop of active-reactive power control, and the input power adjustment module is connected with the The power loop connection of the active-reactive power control; the input power adjustment module adjusts the input power command of the active-reactive power control according to the grid voltage of the receiving end and the DC bus voltage of the receiving end. With the present invention, reactive power can be continuously provided to the power grid when the voltage drops in the power grid at the receiving end, and no overcurrent phenomenon will occur in the converter station. DC bus voltage, the system can operate stably after the fault is restored.

Disclosed are a control circuit, a control method and a resonant converter. By generating a start control signal that changes correspondingly following the duration of the soft start process as a loop variable, the loop variable presents different changing trends when the resonant current intensity is in different intervals, and then controls the converter so that the The resonant circuit starts. Therefore, according to the actual situation of the resonant circuit current, the change speed of the soft-start loop variable is dynamically adjusted, so that the resonant circuit can start quickly without causing the resonant circuit current to over-current. Resonant circuit design process.

The invention discloses a mixed bipolar DC transmission system. The system comprises a rectification converter station and an inversion converter station which are connected through a DC transmission line, wherein the rectification converter station is formed by two thyristor converters through serial connection, and the serial connection node is grounded; and the inversion converter station is formed by two modular multilevel converters (MMCs) through serial connection, the serial connection node is grounded, and positive and negative ends after serial connection are connected with one-way connection power devices. The system has the advantages of low cost and loss, high reliability and the like of the existing thyristor converter, flexible control of the MMCs, low harmonic, active-reactive power decoupling control, low dependence on an alternating current system and the like; and the system is divided into positive and negative poles, so that operating reliability is strengthened, and the power devices provided with the one-way connection capacity and additionally arranged at outlets of inverters can effectively handle DC faults. The system is suitable for occasions such as high-power long-distance high-voltage DC transmission and island current delivery, provided with broad development space, and worthy of being popularized vigorously.

The invention discloses a double-damping mixed star connection vibration-free brake frequency conversion device comprising a frequency converter including a main control circuit; the double-damping mixed star connection vibration-free brake frequency conversion device also comprises two damping circuits and two solenoid valves; three output ends of each damping circuit are connected in series with a solenoid valve and correspondingly connected with three output ends of an inversion circuit; an control input end of the solenoid valve is connected with a damping control signal output end of the main control circuit; each damping circuit comprises three resistors and three capacitors, one resistor and one capacitor are connected in parallel to form a damping unit, and three damping units of each damping circuit are all in star connection. The resistors and the capacitors in the damping circuit are employed to consume the energy on the output end, i.e., the load end of the inversion circuit, thereby obtaining the purposes of no vibration, no noises, on overvoltage, on overcurrent, and no temperature rise brake; the main control circuit is employed to realize automatic control, and the double-damping mixed star connection vibration-free brake frequency conversion device is an updated product of a conventional poleless speed adjusting frequency converter.

The invention discloses a method and system for controlling energy of a two-motor controller with a boosting apparatus. The method comprises the following steps: calculating surplus power by virtue of current parameters, ensuring the output power of one motor system of the two-motor controller in priority according to a current working mode and state, feeding back an allowable output torque of the motor system in real time, and ensuring a first motor system and a second motor system not to have over-current phenomenon in an application process. A maximum demand of an entire car can be satisfied, and the maximum output performance of the two-motor controller is played. In addition, current value is adopted for calculation, so that time delay is reduced, and the over-current fault of the two-motor system or the risk of damaging the two-motor system are reduced.

The invention provides a direct-current transformer which is located between a low-voltage direct-current bus and a medium-voltage direct-current bus and comprises a plurality of direct-current voltage transformation subunits. The input ends of a plurality of direct-current voltage transformation subunits are connected in sequence and are connected with the low-voltage direct-current bus; the output ends of a plurality of direct-current voltage transformation subunits are connected in sequence and are connected with the medium-voltage direct-current bus; each direct-current voltage transformation subunit comprises a DC / DC converter and a fault isolation voltage balancing module; the input end of the DC / DC converter is connected with the low-voltage direct-current bus, the output end of theDC / DC converter is connected with the input end of the fault isolation voltage balancing module, and the output end of the fault isolation voltage balancing module is connected with the medium-voltage direct-current bus; the mass and the occupied area are small, and the cost is low; the number of layers of the direct-current voltage transformation subunits is greatly reduced, the occupied area isreduced, the cost is saved, and the application scene of one-way power flow can be met.