305 results about "Isolation transformer" patented technology

The utility model discloses a soft start system based on excitation current reduction, which is characterized in that a time relay mainly controls the switching of a live wire between a power resistor and an alternating current contactor, the power resistor magnetizes a transformer at the moment of electrification, and the alternating current contactor is connected into a circuit by the time relay after the magnetization is completed; and after the power resistor is short-circuited, the circuit is cut out, so that the purpose of suppressing the excitation inrush current is finally achieved, the excitation effect caused by voltage abrupt change at the power-on moment of the isolation transformer can be avoided, and the excitation abrupt change of the isolation transformer during power-on is effectively reduced.

A motor power source regulation circuit, a control method and an electronic device are provided. The motor power source regulation circuit includes a power factor correction circuit, an isolation circuit, a first power source conversion circuit, a second power source conversion circuit and a control circuit. The isolation circuit includes a first switch sub-circuit and an isolation transformer. The power factor correction circuit regulates an AC input signal to a first DC signal. The first switch sub-circuit converts the first DC signal to a first AC signal. The isolation transformer converts the first AC signal to two or more second AC signals. The first power source conversion circuit converts the second AC signal to a DC drive signal and outputs it to a DC motor. The second power source conversion circuit converts the second AC signal to an AC drive signal and outputs it to an AC motor.

The invention discloses an intelligent switching control electrician practical training identification device, which belongs to the technical field of electrical detection and comprises a practical training platform, an operation panel, an electrical carrier plate and a built-in PLC (Programmable Logic Controller), the system integrates power input, a first conversion unit composed of a first isolation transformer and a first contactor, a second conversion unit composed of a second isolation transformer and a second contactor, a control unit, a data storage module, an operation input unit, a feedback unit and a load output unit. A dual-safety interlocking structure combining software interlocking and contactor hardware interlocking is realized through a PLC, and two paths of power outputs cannot be switched on at the same time. The device has the functions of intelligent mode switching, real-time voltage monitoring, fusing and sudden stop dual protection, operation state feedback and practical training data storage, meets industrial-grade and safety-grade practical training requirements, is compact in structure and high in safety, supports closed-loop control and data tracing, and is suitable for modern electrician skill training and intelligent examination and identification.

The application discloses a novel lung lobe-shaped magnetic shielding partial discharge detection device and a detection method. The device comprises an isolation transformer, a bushing, a detection electrode and a partial discharge instrument. A single-phase power supply is connected with a reactor in parallel, and then connected with an input end of the isolation transformer. One end of an output end of the isolation transformer is connected with the bushing, and then connected with the detection electrode. The other end of the output end of the isolation transformer is grounded. A grounding end of a to-be-detected lung lobe-shaped magnetic shielding is grounded, and the grounding end of the to-be-detected lung lobe-shaped magnetic shielding is connected with the partial discharge instrument. The to-be-detected lung lobe-shaped magnetic shielding and the detection electrode are correspondingly arranged to form an equivalent capacitor and are coupled and connected. The application can be used to determine whether there is a defect in the lung lobe-shaped magnetic shielding by performing a partial discharge test on the lung lobe-shaped magnetic shielding before the lung lobe-shaped magnetic shielding is assembled into a transformer. The application has the characteristics of high test efficiency and low applied voltage, and greatly improves the first-time pass rate of the transformer product provided with the lung lobe-shaped magnetic shielding.

In the DAB converter, the control circuit (13) controls in a manner including a first period in which the first DC portion (E1, Ca) is conducted with the primary winding (n1) of the isolation transformer (TR1), and a second period in which both ends of the primary winding (n1) of the isolation transformer (TR1) are short-circuited within the first bridge circuit (11), in the case of step-down transmission of electric power from the first DC portion (E1, Ca) to the second DC portion (E2, Cb). The control circuit (13) generates: a first mode in which the fourth switching element (Q4) is off, and the first period is switched to the second period; a second mode in which the second switching element (Q2) is off, and the first period is switched to the second period; a third mode in which the first switching element (Q1) is off, and the first period is switched to the second period; and a fourth mode in which the third switching element (Q3) is off, and the first period is switched to the second period.

A flexible loop-closing device and its active power control method are disclosed. The device includes a power electronic transformer and distribution networks connected to both sides. Each phase of the power electronic transformer includes several power modules symmetrically arranged on both sides. Each power module includes an H-bridge section composed of power electronic switching devices T1-T4 and a DAB section composed of power electronic switching devices T5-T8. The power modules on both sides are connected through a resonant inductor Lr and an isolation transformer T. The H-bridge sections of the power modules on the same side are connected in series to the high-voltage AC bus of the distribution network on the same side. The active power control method is as follows: the AC side of the loop-closing device is controlled by a cascaded H-bridge, and the DC side is controlled by a DAB. When there is no active power flow control requirement, the DAB section does not need to work, and the DC bus voltage of the power modules on both sides is controlled by their respective cascaded H-bridges. This method can simplify the operation complexity of the loop-closing device to the greatest extent, ensure the stable operation of the loop itself and the reliability of the system power supply, and greatly reduce the system losses when there is no active power flow control requirement. The active power control strategy proposed in this invention can avoid frequent switching of the cascaded H-bridge control mode, ensure the stable operation of the flexible loop-closing system, and improve the dynamic response speed.

This utility model relates to an electric shock protection safety isolation distribution box, belonging to the technical field of distribution boxes. The electric shock protection safety isolation distribution box includes a distribution box, an air switch installed on the inner wall of the distribution box, an isolation transformer installed on the inner wall of the distribution box, a fixing component installed at the bottom of the isolation transformer, and a branch sealing component installed on the inner wall of the distribution box. This utility model allows adjustment of the distance between two L-shaped brackets by unscrewing a screw on one side and pulling a slider. The slider's sliding distance is adjusted according to the bottom hole position of the replacement isolation transformer. The screws are then tightened to fix the L-shaped brackets to the inner wall of the distribution box. Finally, the new isolation transformer is installed in the corresponding square slot. This improves versatility and flexibility, eliminating the need for custom-made enclosures for different transformers, reducing equipment replacement or upgrade costs, adapting to different power and model requirements, and broadening the applicable scenarios.

The application discloses a kind of transformer intelligent enclosed neutral point protection devices, including maintenance switch, lightning arrester, capacitive voltage divider, filter module, isolation transformer, charge-discharge module, voltage detection module, gap discharge unit, digital control unit;Filter module is used to filter the voltage signal of capacitive voltage divider after voltage division flows into isolation transformer, removes high-frequency signal, retains power frequency or its multiple frequency signal, realizes the distinction of transient overvoltage signal and steady overvoltage signal;Voltage detection module is used to detect the voltage amplitude of four capacitors in charge-discharge module, duration, and real-time transmission detection data to digital control unit, and digital control unit real-time uploads detection data to main control background, control pulse trigger controllable switch opens or closes, control discharge of enclosed discharge gap.The application realizes the accurate identification of transformer neutral point overvoltage type, solves the problem of high misoperation rate of existing device, damage transformer.

The present disclosure describes an isolated communication device and a multi-level encoding method therefor. The isolated communication device includes a transceiver (10) and an isolation circuit (20). The isolation circuit (20) includes an isolation transformer (T1) having a driver-side winding and a line-side winding, a first serial resistor (R11) that is coupled with a first end of the driver-side winding, and a second serial resistor (R12) that is coupled with a second end of the driver-side winding. The transceiver (10) transmits a differential signal through the first serial resistor (R11) and the second serial resistor (R12), and receives the differential signal, bypassing the first serial resistor (R11) and the second serial resistor (R12). The isolated communication device reduces power consumption by arranging serial resistors at the driver side of the isolation transformer, and improve impedance matching and strengthen bulk current injection (BCI) immunity by arranging serial resistors at both sides of the isolation transformer.

The invention belongs to the technical field of combustion equipment, and relates to a plasma ignition system and a using method thereof. The system comprises a plasma generator, a combustor, a power supply system, a carrier working medium system and a cooling water system, an anode and a cathode of the plasma generator are coaxially arranged to form an electric arc cavity and a surrounding cooling water cavity, and the anode is provided with a compressed air inlet and a plasma jet outlet; the plasma combustor is sequentially and coaxially sleeved with a first-stage center cylinder, a second-stage combustion cylinder and an outer wall cylinder from inside to outside, the first-stage center cylinder communicates with the jet flow outlet, and the outer wall cylinder is provided with a pulverized coal inlet; the power supply system supplies power to the generator through the isolation transformer and the rectifier cabinet. The carrier working medium system supplies air to the compressed air inlet; the cooling water system enables demineralized water to circulate in the cooling water cavity. Efficient and stable ignition and low-nitrogen combustion of pulverized coal are achieved, the ignition reliability is remarkably improved, the system service life is remarkably prolonged, and the operation automation level is remarkably improved.

The application discloses a kind of for inhibiting loop current's transformer area flexible interconnection system, wherein, first flexible interconnection device and second flexible interconnection device include DC common mode inductance, parallel four-phase bridge arm, first controller and second controller, two DC common mode inductances are connected to the positive and negative poles of four-phase bridge arm respectively and are respectively as positive and negative DC side port, the midpoint of four-phase bridge arm is respectively as four-phase AC side port, the control pole of the first three-phase bridge arm in four-phase bridge arm is respectively connected to first controller, the control pole of the last phase bridge arm is respectively connected to second controller;First, second flexible interconnection device is connected by positive and negative DC side port, and first, second flexible interconnection device is connected by four-phase AC side port four phase lines of the distribution transformer of first, second distribution transformer area. The application can realize transformer area flexible interconnection without isolation, and solve the technical problem that ground loop current is too large when isolation transformer is cancelled.

The utility model relates to the technical field of axle counting isolation transformers, and discloses an axle counting isolation transformer modularization rapid installation support which comprises a plurality of sets of long module strips, high module strips and wide module strips, and the ends of the long module strips, the high module strips and the wide module strips are all provided with step assembling grooves. The long module strips, the high module strips and the wide module strips are sequentially assembled to form a frame. The multiple groups of long module strips, high module strips and wide module strips can be flexibly assembled according to actual requirements to form mounting brackets with different sizes and structures, so that the mounting process is greatly simplified, and the mounting time is shortened. Meanwhile, due to the adoption of the modular design, the transformer is more convenient to adjust or replace, an operator only needs to disassemble and reassemble the corresponding modules, and does not need to change the whole mounting bracket on a large scale, so that the working efficiency is improved, and the maintenance cost is also reduced.

The invention discloses a trapezoidal wave control method of a double-active-bridge direct-current transformer and related equipment, and relates to the technical field of direct-current transformers. In the double-active-bridge direct-current transformer, the first side of a first active bridge is electrically connected with a first direct-current port, the first end of the second side of the first active bridge is electrically connected with the first end of an auxiliary inductor, and the second end of the auxiliary inductor is electrically connected with the first end of a primary winding of an isolation transformer. The second side of the first active bridge is electrically connected with the second end of the primary winding of the isolation transformer; a secondary winding of the isolation transformer is electrically connected with a first side of a second active bridge, and a second side of the second active bridge is electrically connected with a second direct current port; the method comprises the following steps: controlling an inner phase shift angle of a first active bridge to be a first main phase shift angle, and controlling an inner phase shift angle of a second active bridge to be a second main phase shift angle; the difference value between the second main phase shift angle and the first main phase shift angle is a preset auxiliary phase shift angle. According to the embodiment of the invention, the operation reliability and efficiency of the double-active-bridge direct-current transformer can be improved.

This application relates to the field of transformer technology, specifically to a power electronic transformer with an embedded liquid-cooling channel in the windings. The transformer includes a power conversion module, a high-frequency isolation transformer, and a control module. The input terminal of the power conversion module is used to connect to an input power supply. The high-frequency isolation transformer includes a magnetic core, a primary winding, and a secondary winding. The control module controls the power conversion process of the power conversion module. Specifically, the primary winding and / or the secondary winding includes multiple conductive winding plates. The high-frequency isolation transformer also includes a liquid-cooling plate and an embedded liquid-cooling channel disposed within the liquid-cooling plate. The liquid-cooling plate and the multiple conductive winding plates are stacked, and the embedded liquid-cooling channel contains coolant. This invention enhances the internal heat dissipation capacity of the high-frequency isolation transformer through embedded liquid cooling, better meeting the engineering requirements of high power density, miniaturization, and continuous operation.

The utility model discloses an isolation type voltage sag active protection device, which is arranged between a three-phase full-bridge rectification circuit and a frequency converter direct current bus, and comprises a full-bridge LLC resonant converter, a DSP digital control circuit and an isolation unit, and direct current output by the three-phase full-bridge rectification circuit is converted into stable direct current through the full-bridge LLC resonant converter. The isolation unit is connected with a frequency converter DC bus; wherein the DSP digital control circuit controls on and off of a switching tube in the full-bridge LLC resonant converter by generating a PWM signal. According to the isolation type voltage sag active protection device of the utility model, efficient and stable electric energy conversion is realized through the full-bridge LLC resonant converter and the DSP digital control circuit; and furthermore, through the isolation unit and the high-frequency isolation transformer, effective isolation between the power supply and the load is realized, and the system safety is improved.

The invention provides a silicon carbide power switch driving circuit, and relates to the technical field of power electronic driving, the silicon carbide power switch driving circuit comprises a pulse generation module, an isolation transformer and a driving output module, the pulse generation module converts an input direct current voltage into an alternating pulse voltage with dead time and outputs the alternating pulse voltage to a primary winding of the isolation transformer; the driving output module comprises a charging loop, an active discharge loop and a discharge resistor assembly, the active discharge loop comprises a normally-on switch tube, the control end of the normally-on switch tube is connected with one winding section of the secondary winding, and a discharge path bypassing the secondary winding is provided for the gate-source capacitor in the dead zone time. The discharge resistor assembly comprises a first discharge resistor and a second discharge resistor which are arranged in series and located outside and inside the active discharge loop respectively. The discharge falling edge is effectively accelerated, the contradiction of mutual restriction of the discharge speed and oscillation suppression is solved, the structure is simple, and the cost is low.

The utility model discloses an alternating-current variable-frequency power supply capable of realizing three-phase-to-single-phase full-power output, which comprises a main board, a slow starting module, a three-phase EMI (Electro-Magnetic Interference) filter, an R-phase output isolation transformer, an S-phase output isolation transformer, a T-phase output isolation transformer and a three-to-single interlocking switching contactor, the main board is provided with an output voltage sampling end pin, an output current sampling end pin, an SPP-107, an operation panel removing end pin, a driving signal end pin and a slow start removing end pin, and the main board is connected with the slow start module through the slow start removing end pin. The power supply does not need to additionally purchase single-phase power supply equipment and can be directly switched; compared with a voltage regulator scheme, a variable-frequency power supply is used for supplying power and is isolated from a mains supply power grid, so that the anti-interference performance is improved; an interlocking mechanism is arranged between the single phase and the three phases, so that the single-phase output and the three-phase output are prevented from being mistakenly connected, and the tested equipment is prevented from being damaged.

The invention relates to the technical field of electric appliance control circuits, and discloses a non-isolated zero-crossing detection and commercial power voltage detection multiplexing low-cost simple circuit, which comprises a rectifier diode D3301 of which the cathode is connected with a live wire of a commercial power input end, and the anode is connected with a first resistor R3301; the first resistor R3301, the second resistor R3302 and the third resistor R3303 are connected in series. Through a sampling link formed by a rectifier diode D3301 and series voltage dropping resistors R3301, R3302 and R3303, a zero-cross detection signal is provided for an interruption input end VT at the same time, and a voltage detection signal is provided for an analog input end AD through a divider resistor R3304 and a filter capacitor C3301, so that multiplexing of two types of detection is realized under a non-isolation structure, commercial power detection can be completed without an optocoupler or an isolation transformer, and the detection efficiency is improved. Therefore, devices are reduced and circuits are simplified.

The utility model belongs to the technical field of chargers, and particularly relates to an automatic power-off safety protection device for an electric bicycle charger. In the safety protection device, an alternating current input port of a charger passes through a relay and then enters a rectifier, after rectification, a pulse voltage rectification filtering charging power supply is obtained through an energy isolation transformer and is connected to a storage battery needing to be charged to execute a charging task, and meanwhile the transformer further generates a group of auxiliary power supplies for power supply of the safety system. In addition, the full-power switch is further connected with a safety switch in parallel, the safety switch is a user operation button installed on the surface of the charger shell, a user starts charging through the safety switch, the charger can automatically and thoroughly cut off connection with the alternating-current mains supply through the relay after the storage battery is fully charged, safety is high, and the charger can be widely applied to the technical field of storage batteries.

The utility model belongs to the technical field of electronics, and particularly relates to a low-harmonic rectification control circuit which remarkably counteracts low-order harmonics such as five-order harmonics and seven-order harmonics through multi-phase superposition of a phase-shifting transformer, the total harmonic distortion (THD) is lower than 5%, the environmental protection requirement of high-power industrial equipment for a power grid is met, and a control cable has the advantages of low harmonic pollution, low cost and the like. The DSP main control chip is combined with the digital timer, and the serial-to-parallel circuit only needs one PWM pin and three GPIO pins, so that the DSP resource occupation is reduced; the gating circuit adopts a general multiplexer (74HC4051D), so that the hardware complexity is reduced; the drive circuit realizes strong and weak current isolation through the isolation transformer, prevents high-voltage interference from damaging a control chip, improves the system safety, and reduces the maintenance cost of the circuit.

A transformer assembly is presented, including a first input; a second input; a first output; a second output; a first winding including a first tap, a second tap, a third tap, and a fourth tap, a first switching device having a first input terminal, a first tap terminal coupled to the first tap, a second tap terminal coupled to the second tap, the first switching device being configured to couple the first input terminal to the first tap terminal or the second tap terminal, and a second switching device having a second input terminal, a third tap terminal coupled to the third tap, a fourth tap terminal coupled to the fourth tap, the second switching device configured to couple the second input terminal to the third tap terminal or the fourth tap terminal; and a second winding coupled to the first output and the second output.

The invention discloses a directional breathing maintenance-free high-performance concrete isolation transformer box for an airport navigation aid lamp. The device comprises a box body, a box cover, an air conveying valve, a one-way drainage valve, a water screening grate and a sealing gasket, the box body is of a cylindrical structure with an open upper end, the inner upper part serves as a transformer and cable placement area, the inner lower part serves as a water collection area, and a box bottom opening is formed in the middle of the bottom surface; the one-way drain valve is arranged in the opening at the bottom of the box; the water sieving grate is horizontally mounted in the middle in the box body; the box cover covers the upper port of the box body, and an opening is formed in the middle of the box cover; the gas conveying valve is mounted in the open hole; and the sealing washer is arranged at the contact part of the box body and the box cover. The method has the advantages that the airport operation safety and efficiency can be greatly improved, the airport operation and maintenance cost is reduced, the problem which puzzles airport operation and management all the time is solved, and the method will certainly become a valuable airport infrastructure and has high application and popularization value.

The invention relates to the related technical field of power equipment, and discloses a transformer assembly for distribution network safety isolation, which comprises a main body and further comprises an unlocking mechanism, the unlocking mechanism is arranged on the front surface of the main body, and when a cable is fixed by a worker through a bolt, the unlocking mechanism enables a threaded hole to rotate along with the bolt after the cable is fixed; the reinforcing mechanism is mounted at the bottom of the unlocking mechanism; the reinforcing mechanism increases a clamping force for the cable when the cable is fixed. According to the invention, due to the arrangement of the lotus block, the movable nut can rotate along with the bolt when the cable is fixed, so that the phenomenon of slipping of the bolt is reduced, the service life of the bolt and the movable nut is prolonged, and the safety of the isolation transformer is indirectly improved.

A charging system includes an AC / DC converter a DC / DC converter, and a control circuit. The AC / DC converter is connected between first / second input nodes and first / second intermediate nodes and is connected to an AC power supply via the first / second input nodes. The DC / DC converter is connected between the first / second intermediate nodes and first / second output nodes and is connectable to a battery via the first / second output nodes. The DC / DC converter includes an isolation transformer, a primary circuit, and a secondary circuit. The primary circuit includes switching elements. The control circuit causes the switching elements to start operation at a first frequency when the AC / DC converter and the DC / DC converter are activated, and causes the switching elements to operate at a second frequency when the AC / DC converter and the DC / DC converter are in steady operation. The first frequency is higher than the second frequency.

The invention discloses an electric energy meter and electricity utilization acquisition terminal detection table body power supply device and a control method, and relates to the field of electric energy meter and electricity utilization acquisition terminal detection. The power supply device comprises a power source, an isolation transformer, a control unit and relays in one-to-one correspondence with meter positions, the isolation transformer is connected with a power grid and connected with normally-closed contacts of the relays, the power source is connected with normally-open contacts of the relays, and common ends of the relays are connected with meters. The control method comprises the following steps: during electrification, normally closed contacts of all relays are closed, and all meters are powered and started by an isolation transformer; and after the meters and the power source are stabilized, the control unit executes an equal phase-zero voltage time-sharing switching control strategy and controls the relay to act in a time-sharing manner, so that the meters are sequentially switched to the power source to supply power. Through cooperation of the isolation transformer and the power source and accurate zero-crossing switching, multi-meter-position stable starting is achieved while the power source is prevented from being impacted by surge, the loading capacity and the detection efficiency of a detection table body are effectively improved, and the equipment cost is reduced.

The invention discloses a three-phase dry-type isolation transformer, which belongs to the technical field of transformers, and comprises a winding, an upper yoke fixing structure and a lower yoke fixing structure are respectively arranged above and below the winding, a first plate body with air holes is arranged at the bottom of the winding, and a first rod body is arranged at the bottom of the first plate body; the bottom of the first rod body is connected with a bottom frame through a vertically-arranged first support. According to the scheme, the problems that traditional natural convection heat dissipation and existing equipment are poor in adaptability and complex in structure are solved, and the device is stable in operation and long in service life.

The invention relates to the technical field of power electronics, and provides a power switching device quick turn-on and turn-off circuit for transformer isolation driving, which is connected between an isolation transformer and a power switching tube and comprises a turn-on acceleration network and a turn-off acceleration network, the turn-on acceleration network comprises a first resistor and a first capacitor which are connected in series, and the turn-on acceleration network is arranged on the primary side of the isolation transformer after being connected with the main driving circuit in parallel; the turn-off acceleration network comprises a first diode and a first triode, the cathode of the first diode is connected with the grid electrode of the power switch tube and the emitter electrode of the first triode, the anode of the first diode is connected to the base electrode of the first triode, the collector electrode of the first triode is connected with the secondary ground, and the base electrode of the first triode is connected with the biasing circuit. Receiving a turn-off control signal source through a biasing circuit; according to the invention, the problems of low switching speed, waveform distortion and reliability reduction caused by parasitic parameters of the transformer can be effectively solved.

The invention belongs to the technical field of converters, and relates to an interlaced totem pole type AC-DC converter and a magnetic bias current sharing suppression control method, and the AC input of the converter passes through an LC filter and then is connected to a primary side switching network; the primary side switch network adopts a totem pole and double active bridge arm multiplexing structure; the primary side of the isolation transformer is bridged between the central points of the first bridge arm and the second bridge arm of the primary side switching network through a power transmission inductor; a secondary winding of the transformer for secondary rectification output is connected to a full-bridge rectification circuit consisting of two bridge arms to directly supply power to a direct-current load; through the collaborative design of triple closed loops of main power, current sharing and magnetic biasing, the core problems of power transmission, current balancing, magnetic biasing of the magnetic core and the like are systematically solved. Each loop adopts a hierarchical bandwidth design based on the physical coupling relationship and the disturbance characteristic, so that the global stability is ensured, the rapid dynamic response is obtained, and the cooperative control is realized.

This invention relates to a low-power isolated remote communication power supply system, comprising a power transmitting end and a power consumption terminal arranged on a communication bus. The power consumption terminal includes a data transmitting module, a data receiving module, a rectifier and filter module, and a second isolation transformer. The primary side of the second isolation transformer is connected to the communication bus, and the secondary side is connected to the output of the data transmitting module, the input of the data receiving module, and the input of the rectifier and filter module, respectively. The power transmitting end includes a power switching circuit and a switch control circuit. The input of the power switching circuit is connected to a DC power supply, and the control signal input is connected to the switch control circuit. The power transmitting end also includes a first isolation transformer and a low-pass filter. The output of the power switching circuit is connected to the primary side of the isolation transformer through the low-pass filter, and the secondary side of the isolation transformer is connected to the communication bus. Compared with the prior art, this invention, while transmitting power based on the communication bus, can report communication window time, etc., when supporting more power consumption terminals.

To suppress biased magnetization of a magnetic core in a magnetic component such as an insulating transformer connected between bridge circuits.SOLUTION: A control device that generates a first driving pulse to be supplied to a first bridge circuit and a second driving pulse to be supplied to a second bridge circuit, the control device operating only one bridge circuit of the first bridge circuit and the second bridge circuit in a state where a power transmission operation is not performed between the first bridge circuit and the second bridge circuit to detect a variation in a delay time of a timing at which a state of each of switching elements included in the one bridge circuit changes, wherein a timing at which the driving pulse supplied to the one bridge circuit among the first driving pulse and the second driving pulse is changed is corrected according to the variation.SELECTED DRAWING: Figure 1