424results about How to "Reduce inrush current" patented technology

The invention is a multi-end flexible direct current transmission system and a starting method thereof. The multi-end flexible direct current transmission system and the starting method thereof comprise two sending end converter stations and a receiving end converter station. A wind power plant is connected with the two sending end converter stations. The two sending end converter stations convert electric energy into direct current and transmit the direct current to the receiving end converter station though a direct current transmission line. The receiving end converter station converts the direct current into alternating current and is connected with a large power network. A first sending end converter station in the two sending end converter stations is connected with a second sending end converter station and the receiving end converter station through a direct current disconnecting switch (Sdc1). The second sending end converter station is connected with the first sending end converter station and the receiving end converter station through a direct current disconnecting switch (Sdc2). The receiving end converter station is connected with the first sending end converter station and the second sending end converter station through a direct current disconnecting switch (Sdc3). The starting procedure of the multi-end flexible direct current transmission system and the starting method thereof is stable and has a safe and reliable property and a wide range of application. The multi-end flexible direct current transmission system and the starting method thereof is used for multi-end flexible direct current transmission projects with modularization multi-end flat topological structures, and can decrease impact current on alternating current side or direct current side at the moment of deblocking of multi-end converter stations, and can stably generate direct voltage to a rated value.

The invention relates to a boosting method for synchronization without insulating photovoltaic grid-connected inverters. The inverter operates independently before the integration into the grid. The AC switch is kept disconnected while the DC voltage sensor detects the value of voltage amplitude of the DC bus input by the inverter. The AC voltage sensor detects the amplitude, frequency and phase of the grid voltage. When the voltage amplitude input into the DC bus by the inverter exceeds the peak voltage of the grid, the inverter manages the circuit to calculate, according to the voltage amplitude of the DC bus and the amplitude, frequency and phase of the grid voltage, and get the inverted modulating wave that is synchronized with the phase and frequency of the grid voltage. When the DC inverter voltage and the grid voltage become identical in frequency, phase and amplitude, and the voltage amplitude of the bus is permissible for the synchronization, the inverter controls the circuit and the actuation of the AC switch and starts the operation of the synchronization. The invention is simple in structure and can save power as well as enhance the system stability.

A LED dimming control circuit that avoids a higher output voltage than expected is provided. The LED dimming control circuit comprises an inductor, a transistor, a dimming control signal, a feedback signal, a switching control circuit, an error amplifier, and an inverted amplifier. The inductor and the transistor are coupled to a node. The switching control circuit is controlled by the dimming control signal and the feedback signal. The transistor is controlled by the switching control circuit. The output terminal of the error amplifier and the non-inverted input terminal of the error amplifier form a negative feedback path via the inverted amplifier.

A discrete frequency conversion start-up system of the alternating current impression electromotor and its start-up method. It includes mutual inductor, amplifier, crystal brake, processor, liquid crystal screen, chip machine and keyboard. The steps are as follows: program initialization, detect the initial follow current angle, set the trigger angle of the discrete frequency conversion frequency and make the minimal trigger angle larger than initial follow current angle; frequency division trigger subprogram, frequency division trigger subprogram, frequency division trigger subprogram, frequency division trigger subprogram, frequency division trigger subprogram and flexible start-up subprogram. The invention can make the three-phase alternating current induction motor start up normally when it is heavily loaded and fully loaded.

The invention relates to a combined controller of an LLC series resonant converter. It includes a bridge circuit, the bridge circuit drives a resonant network, a transformer, a frequency modulation controller, a duty cycle controller, an output rectifier circuit, an output voltage detection circuit and an output current detection circuit, the resonant network is connected in series with the primary side of the transformer, and the resonant The network is connected in series between the midpoint of the bridge circuit and the transformer, the filter capacitor is connected in parallel at the output end, the output voltage sampling circuit samples the output voltage value and sends it to the frequency modulation controller and the duty ratio controller, and the output current detection circuit samples the output current value at the same time sent to the duty cycle controller. The driving waveform is comprehensively adjusted by the frequency modulation controller and the duty cycle controller and sent to the bridge circuit for voltage regulation. The invention realizes the low-frequency narrow starting pulse, reduces the impact current of the power switch when starting; realizes the low-frequency narrow starting pulse work under no-load, deep current limiting and short-circuit working conditions, reduces the impact current of the power switch, and reduces the driving loss.

The invention discloses a method for starting hybrid MMC (Modular Multilevel Converter) including full-bridge submodules, and belongs to the technical field of flexible high-voltage direct-current power transmission. The method comprises an uncontrolled charging stage and a controlled charging stage, wherein at the uncontrolled charging stage, all the submodules are locked, and capacitors in the submodules are charged by an alternating-current power grid. At the end of the uncontrolled charging stage, the controlled charging stage is entered, a current converter is unlocked, a closed-loop control loop is added to control submodule switch tubes, and submodule capacitors are further charged to a rated voltage. A starting process is finished when voltages of all submodule capacitors reach therated voltage and a direct-current side voltage reaches a rated direct-current bus voltage. By adopting the method, the current converter is controlled to run under an increased voltage at the controlled charging stage by means of the negative level output capabilities of the full-bridge submodules, so that an alternating-current side output voltage is increased; impact current of the alternating-current power grid in a charging process is reduced; a current-limiting resistor is switched off under low current; and influence on the service life of a power device is avoided.

The invention relates to a starting method for a current transformer, and is applied to the current transformer of which a main circuit is formed by sequentially connecting a direct current (DC)/DC conversion circuit and a DC/alternating current (AC) conversion circuit. A DC bus capacitor is arranged between the output end of the DC/DC conversion circuit and the input end of the DC/AC conversion circuit. The method comprises the following steps of: connecting an AC power grid with the DC end of the main circuit by a current limiting resistor, charging the DC bus capacitor by utilizing the AC power grid, regulating the main circuit to make the amplitude and phase of the output voltage of the main circuit are the same as those of the voltage of the AC power grid to meet grid connection requirements, and connecting the AC end of the main circuit to the AC power grid. By the starting method for the current transformer, not only relatively lower starting current is ensured to make radiation designing easier to realize, but also synchronous grid connection is realized to make grid connection impact current relatively lower; and the method is particularly applied to the starting of a DC double-channel or multi-channel current transformer.

The invention discloses a distributed-generation three-phase inverter smooth switch control method. The method includes smooth switch control over two parts from isolated island operation to grid-connected operation and from the grid-connected operation to the isolated island operation. A smooth switch control link is mainly composed of a phase-locked loop (PLL) and a switch. When an inverter is switched from the isolated island operation to the grid-connected operation, output voltage of the inverter is subjected to presynchronization by operating the switch, so that the output voltage and grid voltage of the inverter are synchronized, current impacting during grid connection is reduced, and smooth grid connection switch is realized; when the inverter is switched from the grid-connected operation to the isolated island operation, reference instruction controlled by current are gradually decreased to zero form current instruction current by operating the switch, off-grid operations have no effect on a system since the grid-connection current is dropped to zero before disconnection of the grid connection switch, the output voltage of the inverter cannot fluctuate, and off-grid smooth switch is realized. With the method, dual-mode smooth switch operation of the distributed generation system is realized.

The invention provides an auxiliary converter for a rail train and a start control method thereof. The auxiliary converter comprises a sampling unit connected with a converter module and is used for acquiring current and voltage of the converter module; the converter module comprises a converter unit, and a pre-charge and output switch control unit connected between an alternating current bus andthe converter unit; the sampling unit, the converter unit and the pre-charge and output switch control unit are respectively in communication connection with a controller; an output contactor connected between an alternating current filter unit and the alternating current bus is arranged in the pre-charge and output switch control unit, and the pre-charge and output switch control unit can pre-charge the converter unit and controls the output contactor to be closed or disconnected after the auxiliary converter is started and before the auxiliary converter is connected to the alternating current bus. According to the auxiliary converter for the rail train provided by the invention, an impact current of a filter capacitor during the starting of the auxiliary converter can be effectively reduced, and grid-connected conflicts can be eliminated, so that the control logic of a central control device is simplified, and the safe and smooth grid connection of the auxiliary converter are realized.

The invention belongs to the field of electric welding and particularly relates to an arc striking pulse peak current control electric welding machine and a control method thereof. The electric welding machine applies a low-frequency low-duty-ratio pulse current during short circuit, and an arc striking pulse peak current of the low-frequency low-duty-ratio pulse current ranges from a 30A welding current to a triplex welding current. Therefore, the arc striking pulse peak current can be higher than the welding current during the low welding current, and arc striking is facilitated; and the arc striking pulse peak current can be lower than the welding current during the high welding current, a short-circuit limit output circuit is cut off after arc striking in welding is successful, the welding current slowly rises from the minimum current to the welding current, and the striking current can be reduced by the means.

A system for reducing inrush current in a three phase utility transformer upon energization of the transformer by an applied three phase voltage utilizes a pre-flux circuit for establishing residual flux levels in the core segments of the primary windings of the transformer which are near the prospective flux levels established in the core segments by the applied voltage. The pre-flux circuit includes a pre-fluxing capacitor which, after being charged to a predetermined voltage level, is discharged serially through two of the primary windings to establish the predetermined flux levels in the core segments of the two windings, and a reduced flux level in the core segment of the remaining primary winding. The transformer is energized at the instant of positively-referenced peak phase voltage to the third primary winding such that prospective and residual flux approach a near-equal level in all three core segments and inrush current is reduced. The method may be applied to the secondary or tertiary windings instead of the primary windings. Additionally, an alternative method allows application of the pre-fluxing circuit to a delta-connected set of transformer windings.

The invention discloses an intelligent control method for strong oil air cooling of a transformer, which comprises the following steps: step a: the program starts, initializes, and then turns into a main program for circulating operation; B, sample and processing that upper oil temperature of the transform; C, judge that sampling temperature in the step b; Step d: if the oil temperature judged instep c is greater than the upper limit temperature, the fan automatically switches on and off subroutine 1; If the oil temperature judged in the step c is less than the upper limit temperature, the fan automatically switches on and off the subroutine 2; E, sending that temperature signal and the running program to a liquid crystal screen for display; (f) send that upper oil temperature of the current transformer and the operation condition of the fan to the upper compute through a remote communication program; Step g: End the current program and return to step b. The invention has the advantages that the problems that the prior art is not conducive to energy saving and effective utilization of equipment, and the air cooling device is frequently switched on and off are solved.

The invention discloses a base region gradient P<+>-N-N<+> type SiC ultrafast recovery diode manufactured on a 4H type single crystal silicon carbide epitaxial layer and a process. An anode/(P<+>)4H-nc-SiC/(N) slowly changes into a 6H-nc-SiC/(N)4H-c-SiC/(N<+>)4H-c-SiC/cathode. The base region gradient P<+>-N-N<+> type SiC ultrafast recovery diode comprises an N<+> type 4H-c-SiC substrate, an N type 4H-c-SiC epitaxial layer, an N type 6H-nc-SiC gradually-doped and grain-gradient multilayer film and a P<+> type 4H-c-SiC single layer film, wherein the outer sides of the N<+> type 4H-c-SiC substrate and the P<+> type 4H-c-SiC single layer film are in ohm connection with an anode NiAu and an anode TiAu respectively. The device structure is made by using a PECVD (Plasma Enhanced Chemical Vapor Deposition) technology. The process has the advantages of shortening the reverse recovery time, inhibiting surge current and lowering the process temperature.

A fluorescent lamp electronic ballast includes a power factor correction flyback circuit and an inverter ballast circuit. The power factor correction flyback circuit is composed of a rectifier connected to a DC to DC flyback converter. The flyback converter includes a flyback transformer connected to a diode/capacitor combination. The flyback transformer is switched during operation to produce a flyback waveform that is rectified by the diode and results in a DC output at the capacitor. The inverter ballast circuit receives the DC output and converts the DC output to an AC signal for operating the flourescent lamp.

The invention provides an off-grid and grid-connected smooth switching method of a virtual synchronous generator. The smooth switching method is characterized by comprising grid-connected/off-grid and off-grid/grid-connected smooth switching. As for off-grid/grid-connected switching, the switching strategy is added in the off-grid and grid-connected switching process without modifying the control strategy of the virtual synchronous generator, and the reference voltage of the virtual synchronous generator is changed into the command reference voltage from the grid voltage and the correction angular velocity of pre-synchronous control is enabled to be zero directly so as to realize grid-connected/off-grid smooth switching. Popularization of the virtual synchronous generator technology is further facilitated in the field of new energy power generation, and friendly accessing of distributed energy resources can be realized so as to enhance the stability of the electric power system. Besides, application of the control strategy and the theoretical analysis method related to the conventional synchronous generator to VSG is facilitated so as to play an important role in the active power distribution network and the microgrid in the future.

The invention discloses a voltage conversion device with a soft start function. The voltage conversion device comprises a low dropout voltage stabilizing circuit, a feedback module and a soft start circuit, wherein, the soft start circuit comprises a first capacitor, a first resistor, a second resistor and a first diode. The soft start circuit used in the voltage conversion device only composed of driven elements, so the circuit structure is simple and is easy for realizing. Besides, the soft start circuit of the voltage conversion device can delay the start time of the low dropout voltage stabilizing circuit and effectively reduces the electromagnetic interference caused by inrush current further.

The present document relates to a pre-charge circuit of electronic circuits having Miller compensation and significant output capacitance such as LDOs or multistage amplifiers. The pre-charge circuit limits an inrush current right after enabling of the electronic circuit. The pre-charge circuit limits and clamps the fast charging of the Miller capacitor. A delay circuit disables the pre-charge circuit when the bias conditions of the Miller capacitor are close to normal bias conditions.

The invention discloses a soft starting device and method for a high-power transformer. The soft starting device for the high-power transformer comprises a current limiting module, a control module, a first switch module and a second switch module, wherein the current limiting module is connected between a mains supply and the high-power transformer and used for limiting starting current of the high-power transformer; the control module is used for generating first control singles when the high-power transformer performs soft starting and generating second control singles when the high-power transformer performs soft starting to power frequency; the first switch module is connected between the current limiting module and the high-power transformer, is connected according to the first control singles, and is disconnected according to the second control singles; and the second switch module is in parallel connection with the current limiting module, is disconnected according to the first switch module, and is connected according to the second control singles. Disconnection and connection of the first switch module and the second switch module are controlled through the control module, so that the high-power transformer is started smoothly under the conditions of current limiting, and automatic switching between power frequency power supply and frequency conversion power supply of the high-power transformer is further achieved.

The invention relates to a soft start circuit of a converter. The main circuit of the soft start circuit comprises a DC (direct current)/DC converting circuit, a DC/AC (alternating current) converting circuit and a paralleling switch, wherein the DC/DC converting circuit comprises one or more mutually independent DC channels, at least one DC channel is a chopper DC channel on which a DC chopper circuit is arranged; the input end of the DC channel is a load connecting end, the output end of the DC channel is provided with a DC bus capacitor for forming the output end voltage; one or more soft start branches provided with soft start switches are connected between the load connecting end and the power supply connecting end of the paralleling switch; at least one of the one or more soft start branches is provided with a soft start resister, and the at least one soft start branch provided with the soft start resister corresponds to the chopper DC channel. By using the soft start circuit of a converter, the soft start current is small, the thermal design is easier, the paralleling impact current is small, and the soft start circuit can be widely used in the charging process of a DC load.

The invention discloses a power supply seamless switching device and method of an electrified railway traction substation. Four paths of voltages, namely two-phase voltages of buses a and b of a contact network and voltages of a bus I and a bus II of a power supply, and four switching position signals, namely switches 201A and 201B of a low-voltage side of a main transformer 1B and switches 202A and 202B of a low-voltage side of a main transformer 2B are accessed to the switching device. During application, the current running mode of the traction substation is identified according to access quantity, automatic charging is achieved to prepare for switching if the running mode is normal, and discharging is performed to lock a switching function if the running mode is abnormal; three switching modes of parallel automatic switching, parallel semi-automatic switching and series switching can be performed; an optimal switching-on mode can be selected according to a real-time relation between the bus voltages of the power supply and the bus voltages of the contact network during switching on; and six modes of parallel rapid switching, rapid switching, same-phase lead phase angle switching, same-phase lead time switching, residual voltage switching and long delay switching can be performed, and uninterruptible power supply switching of two power supplies of the electrified railway traction substation can be achieved.