Abstract: A system in a vehicle includes a first set of one or more windings and a second set of one or more windings electrically isolated from the first set of one or more windings. The system also includes a first inverter coupled to a battery of the vehicle and the first set of one or more windings and a second inverter electrically separated from the first inverter and coupled to the second set of one or more windings. A universal charger includes an alternative current (AC) charging port and a direct current (DC) charging port. A switch is controlled to close to connect the second inverter to the battery.

Abstract: A Cockcroft-Walton (CW) switching voltage converter is disclosed. This CW switching converter includes a set of capacitors; an inductor coupled between an input voltage source and the set of capacitors; a set of switches; and an N-phase control module coupled to the set of switches. In some embodiments, each switch is controlled by the N-phase control module which is configured to sequentially and periodically effectuate a set of N voltage-conversion phases in a sequence of switching cycles. Note that each switching cycle effectuates a voltage conversion through the set of N voltage-conversion phases, wherein N is the conversion ratio of the CW switching voltage converter. Moreover, the N-phase control module is configured to effectuate a phase transition from a current phase to a subsequent phase when a zero-current switching (ZCS) condition on a given switch is met.

Abstract: A low-voltage DC-DC converter (LDC) includes: an N-phase power circuit configured by connection of N DC-DC converters in parallel between a high-voltage (HV) battery and a low-voltage (LV) battery; and one output capacitor commonly connected to an output of each phase DC-DC converter. Each phase of the N-phase power circuit is controlled in an interleaving manner which delays a phase by 360°/N. Here, each N-phase power circuit is controlled by switching at a frequency of [(a frequency at which the parasitic resistance (equivalent series resistance (ESR)) of the output capacitor is minimized)/N]. The parasitic resistance of the output capacitor of the LDC can be minimized. Accordingly, a lifespan of a battery can be improved and efficiency of the DC-DC converter can be increased through the reduction of the equivalent series resistance (ESR) of the output capacitor.

Abstract: Described herein is a power processing unit (PPU) for use with a Hall Effect Thruster (HET) and a Propellant Management Assembly (PMA) of a spacecraft. The PPU comprises an anode and ignitor supply subsystem that provides anode and ignitor signals to an anode and an ignitor circuit of the HET. The PPU also comprises a valve control subsystem that provides valve control signal(s) to valve(s) of the PMA. The anode and ignitor supply subsystem and the valve control subsystem are each coupled to a low voltage (LV) bus of an electrical power subsystem of the spacecraft. The anode and ignitor supply subsystem includes a step-up DC-DC converter having a transformer that steps-up a voltage of the LV bus to a higher voltage used to produce the anode and ignitor signals. The valve control subsystem is devoid of a transformer. An Electric Propulsion System (EPS) includes the PPU, HET and PMA.

Abstract: A system includes a current transformer including: a primary coil, and a secondary coil including at least two taps; a tap selection circuit; a current measurement apparatus configured to produce an indication of an amount of current flowing in the secondary coil; a power supply electrically connected to a first one of the taps, the power supply configured to receive electrical power from the first one of the taps; and a controller coupled to the power supply and the current measurement apparatus, the controller configured to receive electrical power from the power supply and to control the tap selection circuit based on the indication of an amount of current in the secondary coil.

Abstract: A conveyance system includes a machine having a motor; a source of AC power; a drive system coupled to the source of AC power, the drive system to provide multi-phase drive signals to the motor, the drive system including: a first drive having a first converter and a first inverter, the first convertor including a first positive DC bus and a first negative DC bus; a second drive having a second converter and a second inverter, the second convertor including a second positive DC bus and a second negative DC bus; wherein the first positive DC bus and the second DC positive bus are electrically connected and the first negative DC bus and the second negative DC bus are electrically connected.

Abstract: The configurations of LLC charger and controlling methods thereof are provided. The proposed charger includes a transmitter-receiver (TX-RX) transformer including a TX-matrix core set (TX-MCS) and an RX-MCS, an LLC power stage electrically connected to the TX-MCS, and a rectifier electrically connected to the RX-MCS so as to charge a battery pack with a non-contact power transmission.

Abstract: According to one embodiment, there is provided an inrush current suppression apparatus that suppresses an inrush current generated when shunt capacitors are connected to a power system, the apparatus including a voltage measurement unit measuring power source voltages, a current measurement unit measuring circuit breaker currents, a polarity determination unit determining the polarities of residual voltages, a phase section detector detecting a phase section in which the polarities of the residual voltages match the polarities of the power source voltages, and a circuit breaker closing unit closing the circuit breaker within the phase section.

Abstract: Disclosed are methods and systems for subnanosecond rise time high voltage (HV) electric pulse delivery to biological loads. The system includes an imaging device and monitoring apparatus used for bio-photonic studies of pulse induced intracellular effects. The system further features a custom fabricated microscope slide having micro-machined electrodes. A printed circuit board to interface the pulse generator to the micro-machined glass slide having the cell solution is disclosed. An low-parasitic electronic setup to interface with avalanche transistor-switched pulse generation system is also disclosed. The pc-board and the slide are configured to match the output impedance of the pulse generator which minimizes reflection back into the pulse generator, and minimizes distortion of the pulse shape and pulse parameters. The pc-board further includes a high bandwidth voltage divider for real-time monitoring of pulses delivered to the cell solutions.

Abstract: According to one embodiment, there is provided an inrush current suppression apparatus that suppresses an inrush current generated when shunt capacitors are connected to a power system. The apparatus includes a power supply voltage measurement unit measuring a power supply voltage, a circuit breaker current measurement unit measuring a circuit breaker current, a residual voltage polarity determination unit determining the polarities of three phases of a residual voltage, a specific phase determination unit determining a specific phase, a closing phase detector detecting a closing phase, and a circuit breaker closing unit closing the circuit breaker in the closing phase.

Abstract: An apparatus and system for power conversion. In one embodiment, the apparatus comprises a transformer having a primary winding and a plurality of secondary windings; and a cyclo-converter comprising a plurality of switch pairs for converting an alternating current to an AC current, wherein each switch pair in the plurality of switch pairs (i) is coupled between two lines of an AC output and (ii) has a different secondary winding of the plurality of secondary windings coupled between its switches.

Abstract: A radio frequency (RF) power amplifier (PA) and an envelope tracking power supply are disclosed. The RF PA receives and amplifies an RF input signal to provide an RF transmit signal using an envelope power supply voltage. The envelope tracking power supply provides the envelope power supply voltage based on a setpoint, which has been constrained so as to limit a noise conversion gain (NCG) of the RF PA to not exceed a target NCG.

Abstract: A radio frequency (RF) system includes an RF power amplifier (PA), which uses an envelope tracking power supply voltage to provide an RF transmit signal, which has an RF envelope; and further includes an envelope tracking power supply, which provides the envelope tracking power supply voltage based on a setpoint. RF transceiver circuitry, which includes envelope control circuitry and an RF modulator is disclosed. The envelope control circuitry provides the setpoint, such that the envelope tracking power supply voltage is clipped to form clipped regions and substantially tracks the RF envelope between the clipped regions, wherein a dynamic range of the envelope tracking power supply voltage is limited. The RF modulator provides an RF input signal to the RF PA, which receives and amplifies the RF input signal to provide the RF transmit signal.

Abstract: An inrush current suppressing device includes a residual-magnetic-flux calculating unit configured to retain an interruption characteristic of a breaker and an attenuation characteristic of a magnetic flux that are estimated by measurement, analysis, or the like beforehand, and apply the attenuation characteristic to a magnetic flux value at the time of current interruption obtained based on the interruption characteristic of the breaker to calculate a residual magnetic flux value. The breaker is turned on in a power supply voltage phase in which the calculated residual magnetic flux value and a theoretical value of a steady magnetic flux match.

Abstract: The invention relates to a coupling device (4) for four phases of a multi-phase converter (2). Said coupling device (4) includes four coupling modules (6, 8, 12, 14), each of which encompasses four parallel through-holes. At least one section of a conductor loop (18, 20, 22, 24) for a phase. At least one section of a conductor loop (18, 20, 22, 24) for a phase penetrates a through-hole of a coupling module (6, 8, 12, 14), sections of conductor loops (18, 20, 22, 24) for at least two phases penetrating all four through-holes of a coupling module (6, 8, 12, 14).

Abstract: A current distribution apparatus comprising a common current source arranged to deliver an input current into a plurality of branches such that the input current is distributed into a plurality of individual branch currents, wherein each of the plurality of branches includes an inductive arrangement arranged to form an inductive coupling with an associated inductive arrangement of at least one other associated branch.

Abstract: A smart link in a power delivery system includes an insulator, which electrically isolates a power line, and a switchable conductance placed in parallel with the insulator. The switchable conductance includes switchgear for sourcing, sinking, and/or dispatching real and/or reactive power on the power line to dynamically in response to dynamic loading, transient voltages and/or currents, and phase conditions or other conditions on the power line.

Abstract: A converter system includes a first converter, a second converter, and a first inter-phase transformer. The first converter is electrically connected to the second converter in parallel between a first input terminal parallel end and a first output terminal parallel end. The first inter-phase transformer is disposed at the first input side parallel terminal or the first output side parallel terminal, and the first inter-phase transformer is operable to restrain a circulating current generated by the first converter and the second converter.

Abstract: An AC-DC power converter has a phase-shifting autotransformer based rectifiers and DC capacitors. Soft start of the AC-DC power converter is achieved by designing the autotransformer to operate at a low peak flux density at a point of AC voltage step application (initial turn on). The addition of a controlled impedance segregates capacitor charging from the initial magnetizing process of the autotransformer.

Abstract: A multiphase DC to DC voltage converter which has multiple converter cells which are situated parallel to one another and are clocked with a time offset. Furthermore, it contains one magnetic measuring bridge between the outputs of each two converter cells.

Abstract: The embodiments of the present invention provide a cellular power supply network, an intelligent gateway and a power supply control method thereof. The cellular power supply network further comprises: at least one cellular power supply layer formed by a plurality of transformers connected as a cellular structure. In the embodiments of the present invention, the electricity energy can be transferred from one transformer to another transformer demanding power as needed, so that the power is more reasonably distributed and the energy utilization rate is improved. In the technical solutions of the present invention, when a certain transformer cannot work normally due to a fault, the electricity energy outside the transformer can be introduced into the user of the transformer using the cellular power supply network, so as to keep continuous power usage. Meanwhile, the transformer can be separated from the power supply network for repairing and maintenance.

Abstract: Polyphase converter, comprising a plurality of electrical phases (11 to 16), which can each be driven by switching means (21 to 26), wherein at least one coupling means (31 to 39) is provided, which magnetically couples at least one first phase (11) to at least one further phase (12, 14, 16), wherein at least two phases (11, 12) to be coupled are surrounded at least partially by the coupling means (31), wherein at least one insulating body (72) is provided, which on the upper or lower side thereof accommodates the phases (11 to 16) to be coupled and on which at least one fastening means (74, 76, 90) is provided, which interacts with at least one of the phases (11 to 16) for fastening purposes.

Abstract: A Reactive regulator capable of introducing reactive powers in an AC electrical system in order to satisfy the reactive power demanded by the loads of such electrical system in a gradual way, when demanded, and in as many stages as necessary to improve the efficiency and viability of such electrical system by having ways to vary the voltage on one or more reactive elements through a coupling element, transformer, autotransformer or any other type of variable voltage drive, whose primary is connected to an electrical system through terminals and the secondary is connected to a reactive element through at least one switch, of solid state or not, which allows the connection of a mobile terminal to any of the derivations of the secondary of the coupling device.

Abstract: A method, apparatus, and system in which a neutral deriving transformer incorporates a zig-zag transformer configuration is provided. A zig-zag transformer provides an electrical load with a neutral wire. The zig-zag transformer may be electrically connected downstream of a main AC voltage step-down transformer. Additionally, three phase AC voltage lines can be routed to the zig-zag transformer such that the zig-zag transformer comprises a neutral deriving transformer that electrically connects to a ground conductor. The neutral deriving transformer might not be electrically connected to a neutral conductor of the main voltage step-down transformer. The zig-zag transformer can phase shift each winding by approximately 120 degrees and may derive a neutral for at least one single phase load connected to the zig-zag transformer and one of the three phase AC lines in order to provide a common neutral point that takes the place of a neutral cable that connects back to the main AC voltage step-down transformer.

Abstract: A solar power plant includes at least one photovoltaic module for generating power to be fed in a multi-phase grid. At least one inverter is provided for converting a direct voltage generated by the at least one photovoltaic module into an alternating mains voltage. A mains transformer is coupled to receive the alternating mains voltage from the inverter. The inverter is coupled to a primary side of the mains transformer. A direct voltage source coupled between an output of the at least one inverter and an input of the mains transformer such that a potential of the at least one photovoltaic module is displaced and that a bias voltage is set which is different from zero volts.

Abstract: The invention relates to a power supply arrangement with a first transformer (T1), with at least two secondary-side taps for a secondary-side phase conductor potential and with a tap for a secondary-side neutral conductor potential, wherein in standard operation of the first transformer a rated voltage drops between a first of the taps for the secondary-side phase conductor potential and the tap for the secondary-side neutral conductor potential, and with two power controllers (V1, V2) connecting the taps for the secondary-side phase conductor potential with a phase conductor terminal of an output of the power supply arrangement, wherein the circuit arrangement has on the secondary side of the first transformer (T1) a means (T2) for increasing the voltage above the rated voltage.

Abstract: Ripple cancellation techniques are described for various DC to DC converters having multiple parallel phases with magnetically coupled inductors.

Abstract: Each voltage converting unit outputs a first signal at a first output and second signal at a second output. Each first transforming unit includes a magnetically coupled primary and secondary coil, the first output of each one of the converting units is connected to a primary coil of a different one of the first transforming units, the primary coil of each one of the first transforming units is electrically connected to one secondary coil of another one of the first transforming units. Each second transforming units includes a magnetically coupled primary and a secondary coil, the second output of each one of the voltage converting units is connected to a primary coil of a different one of the second transforming units, the primary coil of each one of the second transforming units is electrically connected to one secondary coil of another one of the second transforming units.

Abstract: A load sensing, high efficiency, modular transformer assembly for use in power distribution networks. The control of each module of the modular assembly of high efficiency transformers results in considerable energy savings when compared to conventional transformers. At least two of the transformers have different efficiencies, one higher than the other, The assembly is controlled according to the requirements of the connected load, with modules being switched in and out of circuit, thereby resulting in a transformer with a higher efficiency than is possible with currently available distribution transformers of equivalent capacity. Connection and disconnection of the transformer modules is accomplished with the use of a purpose designed electronic controller.

Abstract: The present invention is single- and multi-phase power distribution systems comprising a plurality of transformers. Each transformer is connected to another of the transformers, in series (single phase) and in series and parallel (multi-phase). Each transformer has a switch connection movable between an on and an off position according to pre-determined rules.

Abstract: A multi-phase coupled inductor includes a powder core material magnetic core and first, second, third, and fourth terminals. The coupled inductor further includes a first winding at least partially embedded in the core and a second winding at least partially embedded in the core. The first winding is electrically coupled between the first and second terminals, and the second winding electrically is coupled between the third and fourth terminals. The second winding is at least partially physically separated from the first winding within the magnetic core. The multi-phase coupled inductor is, for example, used in a power supply.

Abstract: The invention relates to a device for supplying power to measuring sensors and transmitting a synchronous clock signal thereto, in particular, for a low-voltage switchgear, with a power supply unit (10) whose output signals are transmitted to the measuring sensors via transformers providing the isolation. A quartz-controlled oscillation circuit arrangement (quartz-controlled clock generator) is provided whose output signals are supplied to the power supply unit (10) so that the clock frequency of the power supply unit output signals is the same for the primary sides of the transformers (11, 12, 13), the frequency lying within the operating range of the transformers (11, 12, 13).

Abstract: A solar power plant with a plurality of photovoltaic modules for generating a power to be fed in a multi-phase grid, several photovoltaic strings, which are allocated to different phases, being connected to a primary side of a mains transformer and at least one inverter for converting the direct voltage generated by the photovoltaic modules into an alternating mains voltage conforming to the grid being provided and said mains transformer being provided with a neutral conductor and with a grounded terminal, is intended to be improved in such a manner that the life of the photovoltaic modules, in particular in case of thin-film modules, is increased, allowing for high conversion efficiency of the inverters at low wiring costs. This is achieved in that an additional direct voltage source is inserted between the neutral conductor and ground in such a manner that the potential of the photovoltaic strings is displaced and that a bias voltage is set, which is different from zero volt.

Abstract: A method, apparatus, and system in which a neutral deriving transformer incorporates a zig-zag transformer configuration is provided. A zig-zag transformer provides an electrical load with a neutral wire. The zig-zag transformer may be electrically connected downstream of a main AC voltage step-down transformer. Additionally, three phase AC voltage lines can be routed to the zig-zag transformer such that the zig-zag transformer comprises a neutral deriving transformer that electrically connects to a ground conductor. The neutral deriving transformer might not be electrically connected to a neutral conductor of the main voltage step-down transformer. The zig-zag transformer can phase shift each winding by approximately 120 degrees and may derive a neutral for at least one single phase load connected to the zig-zag transformer and one of the three phase AC lines in order to provide a common neutral point that takes the place of a neutral cable that connects back to the main AC voltage step-down transformer.

Abstract: Each voltage converting unit outputs a first signal at a first output and second signal at a second output. Each first transforming unit includes a magnetically coupled primary and secondary coil, the first output of each one of the converting units is connected to a primary coil of a different one of the first transforming units, the primary coil of each one of the first transforming units is electrically connected to one secondary coil of another one of the first transforming units. Each second transforming units includes a magnetically coupled primary and a secondary coil, the second output of each one of the voltage converting units is connected to a primary coil of a different one of the second transforming units, the primary coil of each one of the second transforming units is electrically connected to one secondary coil of another one of the second transforming units.

Abstract: The present invention relates to a control device and a control method of a high voltage inverter capable of automatically and accurately setting up neutral point information at a master controller and a plurality of cell controllers of the high voltage inverter, wherein a master controller determines information of neutral point set up to itself and performs a communication with the cell controllers each disposed at each of a plurality of U phase unit cells, a plurality of V phase unit cells and a plurality of W phase unit cells to determine the neutral point information preset on the cell controllers and to detect a cell controller set up with neutral point information different from that of the master controller, and to correct the neutral point information of the detected relevant cell controller using the neutral point information set up in the master controller, thereby operating the high voltage inverter.

Abstract: A zigzag autotransformer includes a zigzag transformer including first, second and third magnetic cores and an auxiliary winding set including respective pairs of series-connected windings on respective pairs of the first, second and third magnetic cores, the pairs of series-connected windings having respective first terminals connected to respective AC input phase terminals of the zigzag autotransformer and respective second terminals configured to provide respective AC output phases.

Abstract: A device for control of power flow in a three-phase ac transmission line. The device includes a series transformer unit, a shunt transformer unit, and a reactance unit.

Abstract: The invention relates to a method for supply to a magnetic coupler comprising several pairs of windings, each pair being formed from a first and a second adjacent paired winding, magnetically coupled to each other by means of a core of magnetic material. The method further consists of supplying the first winding of each pair with a supply voltage or current out of phase by an angle a with relation to the supply voltage or current for the second winding of the same pair. The absolute value of the angle a is greater than or equal to 4p/N for at least one pair of windings.

Abstract: A load sensing, high efficiency, modular transformer assembly for use in power distribution networks. The control of each module of the modular assembly of high efficiency transformers results in considerable energy savings when compared to conventional transformers. The assembly is controlled according to the requirements of the connected load, with modules being switched in and out of circuit, thereby resulting in a transformer with a higher efficiency than is possible with currently available distribution transformers of equivalent capacity. Connection and disconnection of the transformer modules is accomplished with the use of a purpose designed electronic controller.

Abstract: A transformer power splitter has a plurality of output ports and an input port. The transformer power splitter includes a plurality of primary winding conductors and a plurality of secondary winding conductors. The secondary winding conductors are electrically connected to the output ports respectively. Each of the secondary winding conductors is electrically connected between a positive terminal and a negative terminal of a corresponding output port. The primary winding conductors are magnetically coupled to the secondary winding conductors respectively. The primary winding conductors are configured in a topology including series and parallel connections between a positive terminal and a negative terminal of the input port.

Abstract: A power converter includes an isolated or a nonisolated current-doubler rectification circuit including two magnetic circuit elements, each magnetic circuit element formed with a primary winding and a voltage-sensing winding. The primary windings are coupled in series. The voltage-sensing windings are also coupled in series but with a coupling sense opposite from that of the primary windings. A properly sized inductor and capacitor are coupled in series with the voltage-sensing windings to produce a ripple-cancellation current with slope opposite to a net slope error of currents produced in the two magnetic circuit elements. The current-doubler rectification circuit is preferably coupled to a rectangular ac input waveform. By sensing a scaled voltage difference between two magnetic circuit elements, a very low level of output ripple is produced by the circuit with very low power losses over a range of operating conditions.

Abstract: A sequence of series-connected transformers for transmitting power to high voltages incorporates an applied voltage distribution to maintain each transformer in the sequence below its withstanding voltage.

Abstract: In a multi-phase power converter, efficiency is increased and ripple reduced while maintaining transient response and dynamic performance improved by electrically coupling secondary windings of transformers or provided for inductors of respective phases such that current to a load is induced in each phase by current in another phase. Magnetic coupling can also be provided between phases using a multi-aperture core of a configuration which minimizes primary winding length and copper losses. Efficiency at light load is enhanced by controlling current in the series connection of secondary windings in either binary or analog fashion.

Abstract: A transforming apparatus automatically adjusting the voltage of three-phase power supply comprising three input terminals, three output terminals, a Y-connection three-phase transformer, a switch group, and a switch switching circuit. The three input terminals are respectively connected to three main lines of the three-phase power supply, and the three output terminals are connected to a load installation. The Y-connection three-phase transformer comprises a core, an R-phase winding circuit, an S-phase winding circuit, and a T-phase winding circuit. In the R-phase winding circuit, an R-phase main winding, an R-phase first auxiliary winding, an R-phase first switch, an R-phase second auxiliary winding, and an R-phase third auxiliary winding are serially connected in that order between the input terminal Rin and a neutral point O, the output terminal Rout being connected to the other end of the R-phase main winding.

Abstract: There is disclosed a voltage summer including a transformer having a primary side and a secondary side, wherein a first voltage to be summed is connected to the primary side and a second voltage to be summed is connected to the secondary side. There is further disclosed a transformer comprising a primary winding and a secondary winding and having a turns ratio of primary winding to secondary winding of x:y, providing x turns in series in the primary winding and providing y turns in series in the secondary winding; providing an equal number of turns in the primary and secondary windings; and closely coupling each primary winding turn with a secondary winding turn.

Abstract: A voltage regulator is provided that includes a plurality of buck-boost transformers each having primary and secondary windings. The secondary windings of the transformers are electrically disposed in series between a source and a load. Each transformer is controlled by a plurality of control switches configured to control the voltage across the primary winding of a corresponding transformer. A controller monitors the output voltage and generates control signals for the switches. The transformers generate different voltage level changes in between the source and load and the voltages across the primary windings are capable of assuming opposite polarities to enable scaling of resolution and range. The voltage regulator efficiently regulates power with relatively few or no moving parts and also partially protects the power switching components by removing them from the path of the load current thereby producing a device that is smaller in size, costs less and is more reliable.

Abstract: An inductive element for transforming and/or regulating voltage input from a multi-phase, interleaved power supply system into an output voltage to a load is disclosed. The multi-phase, interleaved power supply system includes a plurality of pulsed power sources, each of which is adapted to provide voltage at a discrete phase. The inductive element includes a magnetic core having, for each power supply, a distinct area of relatively-high magnetic reluctance, which is surrounded by areas of relatively-low magnetic reluctance, and a pair of windings. Each of the pair of windings includes a first, phase winding that is electrically coupled to an output of one of the pulsed power source and to the load, and a second, loop winding that is operatively coupled and proximate to the first, phase winding. Each of the second, loop windings is disposed serially on a closed loop.

Abstract: An exemplary switching power supply circuit (2) includes a power source (20), a pulse width modulation (PWM) circuit (21), a first switching circuit (22), a second switching circuit (23), a first transformer (25), and a second transformer (26). The first switching circuit includes a first transistor (221) and a second transistor (222). The second switching circuit includes a third transistor (231) and a fourth transistor (232). The first transformer includes a first primary winding (251) and a second primary winding (252), and the second transformer includes a third primary winding (261) and a fourth primary winding (262). The switching circuits are controlled by pulse signals from the PWM circuit. When the first and third transistors are switched on, the power source, the first primary winding, and the first transistor form a first closed loop. The power source, the third primary winding, and the third transistor form a second closed loop.

Abstract: The invention is a harmonics reduction device for three-phase poly-wire power lines, which can more reliably eradiate harmonics current applied to an electric power system via a neutral line. The invention comprises an electric power system having three-phase poly-wire power lines in order to supply alternating-current (AC) power voltage to a load; a zigzag transformer in which windings connected with three-phase lines in the electric power system are wound through first and second legs, second and third legs, and third and first legs of a core having three legs, respectively, while varying direction of each magnetic flux, and an intermediate point of each winding is commonly connected with a neutral line of the electric power system and that of the load; and an open delta connection portion in which an winding connected with the neutral line of a load side is wound through the three legs so as to be connected with a neutral line of the electric power system.