Abstract: Industrial truck with a charger, an asynchronous machine and a three-phase AC control unit which converts a DC voltage of a battery for the asynchronous machine, the charger having a switching power supply which is connected to the three-phase AC control unit via a transformer, the switching power supply, the three-phase AC control unit and the transformer forming a resonant converter, which converts a mains voltage into a charging voltage for the battery.

Abstract: An inverter for driving a motor includes one or more power stages for producing one or more power signals for energizing the motor, each power stage including first and second III-nitride based bi-directional switching devices connected in series between a DC voltage bus and ground.

Abstract: In one embodiment, a power cell chamber for a drive system includes moveable and fixed portions. The moveable portion includes a rectifier stage to rectify an input signal received from a secondary winding of a transformer to provide a rectified signal and an inverter stage having a plurality of switching devices to receive a DC signal and output an AC signal. This moveable portion can be slidably adapted within a cabinet of the drive system. In turn, the fixed portion includes a DC link having at least one capacitor to receive the rectified signal and provide the DC signal to the inverter stage.

Abstract: The present invention relates to a method and apparatus for power generation, and in particular a method and apparatus for the control of electrical power generation for use primarily with wind turbines. A method of electrical power generation is described including the steps of: receiving power in the form of alternating current; rectifying said alternating current power to direct current power; control said direct current power to produce controlled direct current power; and inverting said near constant direct current power to produce alternating current.

Abstract: A method for operating a traction converter circuit for coupling to an electric DC voltage network is stated, where the traction converter circuit comprises a network converter, which network converter on the DC voltage side is connected with a DC voltage circuit, wherein the DC voltage circuit can be switched to the electric DC voltage network, a transformer with a primary winding and a secondary winding, wherein the network converter on the alternating voltage side is connected with the primary winding of the transformer, a converter unit, which converter unit on the alternating voltage side is connected with the secondary winding of the transformer and where the network converter is controlled by means of a predeterminable network converter control signal (SN) for the setting of the network converter alternating voltage (UG).

Abstract: A lighting ballast is programmable as to input and output parameters. Both operational characteristics and sensed data are used to control the ballast parameters. The ballast is configured to recapture as electrical energy heat produced by the lamp. The ballast is constructed in modular fashion with a power factor correction circuit module and a ballast control circuit module that snap together to achieve a large number of input voltage and lamp type variations with a small number of separate units.

Abstract: A history-independent and noise-immune modulated transformer-coupled gate control signaling method and apparatus provides robust design characteristics in switching power circuits having a transformer-coupled gate drive. A modulated control signal at a rate substantially higher than the switching circuit gate control rate is provided from the controller circuit to a demodulator via transformer coupling. Codes specified by relative timing of transitions in multiple periods of the modulated control are assigned to gate-on and gate-off timing events that control the switching transistor gate(s) and unassigned patterns are decoded as gate-off events, reducing the possibility that a switching transistor will be erroneously activated due to noise. The modulated signal is constructed so that signal history is not required for decoding, eliminating any requirement of a reference clock. Blanking may be employed to conserve power between codes and to avoid mis-triggering due to noise events during power switching.

Abstract: A power converter apparatus, such as an uninterruptible power supply (UPS), includes an inverter having an input coupled to a first DC bus and a second DC bus and configured to generate an AC output with respect to a neutral terminal at a phase output terminal thereof. The apparatus further includes first and second neutral coupling circuits, each configured to selectively couple the first DC bus and the second DC bus to the neutral terminal, and a control circuit configured to cause interleaved operation of the neutral coupling circuits.

Abstract: Apparatus and methods are disclosed for providing VAR compensation using an AC motor drive, in which an off-line motor drive is configured to prevent power transfer to a motor load output, with a line side converter being operated to control a voltage or current in an intermediate circuit for leading or lagging VAR compensation of an AC power system.

Abstract: A switching power supply transmits power between a single front end including electromagnetic interference filtering and power factor correction circuits to an output end at a high voltage and high frequency from which any desired DC voltage or waveform may be readily and directly derived with high efficiency in order to reduce size and weight of components including transformers at the output end and allow greater variety of connection wiring of reduced weight and volume to be used. The high frequency is limited at the low frequency end by the frequency at which significant power can be transferred through, for example, a ferrite core or other transformer of sufficiently low volume to accommodate closely spaced loads or power converters and at the high frequency end by the wavelength in the connection wiring such that 1/10 wavelength is greater than one thousand feet.

Abstract: In one aspect the invention relates to an electrical circuit for use with a generator having an output port, the circuit to modify one of an electric current or voltage from the generator. The circuit includes a rectifier to convert the alternating current from the generator to direct current, the rectifier having a first port and a second port, the rectifier first port in communication with the output port of the generator; and a direct current to alternating current inverter to convert the direct current from the rectifier to alternating current, the inverter having a first port and a second port, the first port of the inverter in communication with the second port of the rectifier. In one embodiment, the generator is a linear alternator positioned within an energy converting apparatus comprising a Stirling engine having a piston such that motion of the piston drives the linear alternator.

Abstract: Method and arrangement in connection with a motor fed with a frequency converter provided with an intermediate voltage circuit. The method comprises steps of feeding motor voltage to the motor along a motor cable with a frequency converter for controlling the motor, rectifying the voltage of the motor cable and restricting the magnitude of the voltage of the motor cable at the end of the motor cable on the side of the motor with a clipper circuit coupled in parallel with the motor, using the rectified voltage for rotating one or more cooling fans of the motor.

Abstract: A non-contact power supply system is provided in which current phases of induction lines are matched. According to the output current of a power supply unit (21) and the power consumption of induction lines (19), a lead time corresponding to a phase difference between the output currents of the induction lines is determined. A signal for driving transistors (52) is advanced ahead of a drive synchronization signal (?) according to the lead time.

Abstract: A power converter includes: a converter (1) which rectifies an AC power; capacitor series assemblies (2A, 2B) connected to the DC side of the converter; an inverter (3) which assumes that one end of the capacitor series assemblies is at a high potential, the other end is at a low potential, and a series connection point is at an intermediate potential and selects one of the high potential, the intermediate potential, and the low potential for output of a 3-phase AC; an inverter control unit (4) which controls the inverter (3); and a voltage measuring device (8) which measures a capacitor voltage Vdc as a voltage between the both ends of the capacitor series assemblies (2A, 2B). The inverter control unit (4) has a beatless control unit (21) which controls the modulation ratio ? in accordance with a capacitor voltage Vdc and a frequency fixation unit (22) which fixes the frequency of the AC voltage outputted by the inverter (3) to an instruction value.

Abstract: A power conversion system includes a first power converter converting AC to DC, a second power converter converting DC to AC, a current detector detecting output current of the second power converter, a pulsation detector detecting a pulsating component associated with the AC to DC conversion of the first power converter from a pulsating component contained in at least any one of effective power, power, and apparent power of the second power converter, a voltage corrector outputting a correction amount correcting at least one of phase, frequency, and amplitude of a voltage output from the second power converter based on the pulsating component from the pulsation detector, and a voltage controller outputting a voltage instruction to be output from the second power converter based on the correction amount from the voltage corrector, wherein the second power converter converts DC to AC based on the voltage instruction from the voltage controller.

Abstract: The present invention relates to a wind turbine facility comprising a power generator operationally connected to an AC/AC converter adapted to receive variable frequency AC-power from the power generator, and adapted to generate substantially fixed frequency AC-power. The wind turbine facility further comprises a harmonic filter system, and a grid transformer comprising a primary winding being operationally connected to the AC/AC converter, and a secondary winding adapted to be operationally connected to an associated, substantially fixed frequency AC-power supply grid. The grid transformer further comprises a tertiary winding being operationally connected to the harmonic filter in order to suppress unwanted harmonics, such as selected harmonics generated by the AC/AC converter. The turn ratio between the primary and tertiary windings is selected in such a manner that a voltage of the tertiary winding is lower than a nominal voltage level of the associated AC-power supply grid voltage.

Abstract: A control apparatus for an AC-AC direct converter. The control apparatus includes a calculator providing a phase command ?* of an output voltage of the converter, a calculator providing a q-axis current iq by using output currents iu and iw and the phase command ?*, a detector detecting a pulsation component contained in the q-axis current iq, a calculator providing a phase correction magnitude ?cmp so as to decrease the pulsation component, and an adder/subtractor correcting the phase command ?* by using the correction magnitude ?cmp. This apparatus can decrease the output voltage distortion and low frequency torque pulsation and can suppress the increase of an output current without weakening a magnetic flux, even when the converter is operated in an overmodulation region.

Abstract: An improved choke assembly for a power electronics device is provided. More specifically, a choke assembly with improved protection from environmental conditions such as dirt and water is provided. An improved choke assembly may include a double layer of protection around an inductor coil of a choke that seals the inductor coil from the outside environment. Another embodiment may include a choke with a projection that seals the cabinet from the cooling channel while allowing the choke leads to pass into the cabinet.

Abstract: An electric traction vehicle is described herein which may be used to provide power to off-board electric power-consuming systems or devices. The electric traction vehicle may provide 250 kilowatts or more of three phase AC power to an off-board electric power consuming system. The electric traction vehicle may also include an electrical power storage device which can be selectively discharged to allow the vehicle to be serviced.

Abstract: The switching rectifier and switching inverter on a motor drive unit are modulated to indirectly change the magnitude of current and voltage stored in DC link by controlling the magnetic field of the motor to correct for both power factor lead and power factor lag over a wide range of motor speeds and conditions while maintaining a predetermined motor operating point.

Abstract: Capacitors act as bootstrap capacitors of a high side control circuits. The capacitors are charged in a period in which all of high arm switching devices are non-conductive, so-called in a precharge period. When any of U-phase current, V-phase current and W-phase current is smaller than a negative predetermined value (when an absolute value is larger), it is judged which is the largest value. The low arm switching device is turned on only for a phase corresponding to the current of the largest value and the low arm switching devices of other phases are turned off.

Abstract: The present invention provides a three-phase voltage source inverter system capable of obtaining a nearly sinusoidal output waveform while minimizing apparatus size increase and cost increases. The three-phase voltage source inverter system of the present invention is provided with: a three-phase inverter unit INV-M; and an auxiliary circuit 1 inserted between a direct-current power source and the three-phase inverter unit, including: dividing capacitors Cd1, Cd2 dividing a direct-current voltage of the direct-current power source; a single-phase inverter unit INV-A in which 60° ON-periods are set for upper switching elements S7, S8 in each phase of single-phase with an 80° delay, and 60° ON-periods are set for lower switching elements S9, S10 in each phase of single-phase with a 60° delay from the upper side switching elements and with an 80° delay between each phase; and an auxiliary transformer Ta.

Abstract: Power conversion apparatus and methods are presented for providing electrical power to a grid or other load in which a synchronous machine is driven by a wind turbine or other prime mover to provide generator power to a switching type current source converter (CSC), with a current source rectifier (CSR) of the CSC being switched to provide d-axis control of the synchronous machine current based on grid power factor feedback, and with a current source inverter (CSI) of the CSC being switched to provide leading firing angle control and selective employment of dumping resists to dissipate excess generator energy in a fault mode when a grid voltage drops below a predetermined level.

Abstract: A modulated transformer-coupled gate control signaling method and apparatus provides reduction of circuit complexity and robust design characteristics in switching power circuits having a transformer-coupled gate drive. A modulated control signal at a rate substantially higher than the switching circuit gate control rate is provided from the controller circuit to a demodulator via transformer coupling. Power for the demodulator can be obtained by rectifying the modulated control signal at the demodulator, or from another transformer winding. The modulation scheme is chosen to have a DC average value of zero, eliminating any magnetization current management requirements. The modulated control signal may carry redundant control information and/or may encode additional information to provide a more sophisticated gate drive control, such as oversampled gate control information.

Abstract: A method for controlling a rectifier, connected to an AC power network, of a drive converter which is provided with a load-end pulse-controlled rectifier is disclosed. An electronically controlled switch is electrically connected in parallel to every diode of the rectifier. The switching operations of the switches are produced in a manner synchronized with the conduction phases of the associated network-commutated phase voltages and independently of the phase voltages of the supply network. Every switching operation produced is released upon arrival of the next zero value at the rectifier end. The network-end switching operations are linked with the load-end zero values, thereby allowing switching operations to be carried out in a currentless manner.

Abstract: A plasma lighting system comprising a storage unit for storing duty ratios of first and second switching signals according to each material within a bulb by an experiment, a controlling unit for detecting an optimal duty ratio from the storage unit and outputting the first and second switching signals with the same phase corresponding to the detected duty ratio, and a converting unit for converting a direct current voltage into an alternating current voltage consisting of a positive square wave and a negative square wave according to the first and second switching signals, and a method for controlling the same.

Abstract: The invention relates to a method for determining the chance of a disturbance-free operation of a frequency converter (2) connected to a feeding network (18). According to the invention, during the operation of said frequency converter (2), an intermediate circuit voltage (UZK) is continuously measured and a network-side intermediate circuit current (iZKmains) is continuously determined; these measuring quantities are compared with pre-determined operating values of the frequency converter (2), and quantities which are higher or lower than said values are respectively stored; and the frequency (Hij) of said higher and lower measuring quantities is determined and converted into a characteristic number for the quality of the feeding network (18). As said characteristic number decreases, the chance of a disturbance-free operation of the frequency converter (2) increases.

Abstract: A power control interface between an unstable power source such as a wind farm and a power transmission line employs an electrical energy storage, control system, and electronic compensation module which act together like an “electronic shock absorber” for storing excess power during periods of increased power generation and releasing stored energy during periods of decreased power generation due to wind fluctuations. The control system is provided with a “look ahead” capability for predicting power output (wind speed conditions) and maintaining energy storage or release over a “narrow-band” range despite short duration fluctuations. The control system uses data derived from monitoring the wind farm power output and the power transmission line, and employs system-modeling algorithms to predict narrow-band wind speed conditions.

Abstract: A variable speed drive with a converter that is controllable to precharge a DC link is provided. The variable speed drive also includes an inverter. The converter converts a fixed line frequency, fixed line voltage AC power from an AC power source into DC power. The DC link filters the DC power from the converter. Finally, the inverter is connected in parallel with the DC link and converts the DC power from the DC link into a variable frequency, variable voltage AC power. The converter includes a plurality of pairs of power switches, wherein each pair of power switches includes a reverse blocking power switch arrangement connected in anti-parallel to another reverse blocking power switch arrangement. Alternatively, each pair of power switches includes a reverse blocking power switch connected in anti-parallel with a silicon carbide controlled rectifier.

Abstract: A method of controlling connection of an AC power output to a load and power supply grid. The power output is produced by an AC power generating system which includes an AC/AC converter and is independently operable to supply power to the load. The converter is controlled in accordance with a reference generated within the system. To connect the power output to the power supply grid and to supply the load, the reference is replaced by another reference derived from the voltage of the grid, so that the converter is controlled by that other reference, when the power output is connected to the grid and supplies power required by the load. When the power output is disconnected from the grid or loss of the grid voltage occurs, the reference replaces the other reference, and the power generating system operates independently continuing to supply power required by the load without interruption.

Abstract: An apparatus and method for supplying a direct current power source which is capable of compensating a power factor of an input power source by detecting an input current amount according to load changes, the apparatus comprising an input current detecting unit for detecting an input current amount to determine a load size, a power factor control unit for outputting a power factor control signal and an input current amount control signal according to the determined load size, an input current refluxing unit for refluxing the input current by cutting off an input power source based upon the input current amount control signal, an active filter for reducing a harmonic of the input current, rectifying an input alternating current (AC) voltage and boosting a smoothing voltage, a power factor compensating unit for supplying charged energy to the load based upon the power factor control signal, a smoothing unit for smoothing the rectified input AC voltage into a direct current (DC) voltage, and an inverter for conv

Abstract: A method and apparatuses are implemented for electric power systems. An apparatus for power conversion according to one embodiment comprises: a multiple function power converter (77), the multiple function power converter (77) being capable of performing functions of a static inverter, and being capable of at least one of performing functions of a motor controller, and performing functions of a start converter to use a generator as a starter. An architecture system for aircraft according to another embodiment comprises: one or more rectifiers (408), wherein the one or more rectifiers (408) receive at least one high frequency AC power input; and a plurality of power conversion devices (78) optionally connectable to drive at least one high frequency generator (105) as a starter and at least one load, the input of each power conversion device (78) being connected to at least one rectifier (408).

Abstract: A matrix converter (38) converts three-phase AC power input from a first motor-generator (MG1) directly to three-phase AC power for driving a second motor-generator (MG2) and outputs the resultant three-phase AC power, without rectifying the three-phase AC power generated by the first motor-generator (MG1) once to DC power as in an example using a conventional three-phase full-wave rectification inverter. In a power supply system for a vehicle (14), the three-phase AC power is transmitted and received between two motor-generators (MG1, MG2) more directly, by means of the matrix converter (38). Therefore, power loss can be reduced, as compared with a conventional example in which the three-phase AC power is once converted to DC power. Thus, a power supply system for a vehicle with improved energy efficiency and a vehicle including the same can be provided.

Abstract: A matrix converter circuit having two AC/AC matrix converters coupled in parallel in a first mode to power a starter and decoupled in a second mode to each power separate functions used in aircraft power applications. Three common functional modes include 1) start mode with two matrix converters operating in parallel powering the starter, 2) a motor mode where one matrix converter powers a motor, and 3) a constant frequency power mode where the other matrix converter provides constant frequency AC power.

Abstract: In an electric power converter, a main circuit unit and a control unit are detachably attached to each other, and another control unit differing in a control manner can be newly attached to the single main circuit unit. Moreover, the main circuit unit includes a storage unit that stores at least characteristics concerning the main circuit unit, calibration values with respect to the various detectors, a production history, an operation history, and specifications.

Abstract: An inverter apparatus has an adaptable high-resolution voltage-to-frequency (V/f) control. The inverter apparatus receives an analog input signal and includes a first circuit, a second circuit, a third circuit, and a micro-controller unit. The first circuit processes a small-signal portion of the analog input signal with a larger voltage gain. The second and the third circuit both processes large-signal portions of the analog input signal with smaller voltage gains respectively. The three processed analog input signals of the first, the second, and the third circuits are converted into three digital output values respectively. The largest digital output value is selected by the micro-controller unit and supplied to a frequency operation unit for generating a corresponding output frequency.

Abstract: A wind energy converter has a generator adapted to be coupled directly to a wind turbine without need for a mechanical gear unit. A rectifier is coupled to the generator and a converter is coupled to the rectifier to provide a regulated DC bus voltage as a function of a controlled duty cycle. An inverter is coupled to the converter for providing a regulated AC output to a load.

Abstract: A power conversion apparatus is disclosed. In the case where a coil is arranged in a power module, the circuit system between the ends of the coil in the power module, regardless of where the coil is located, is structurally isolated and insulated from each other. This isolation and insulation prevents the capacitance from being created across the coil, and the coil can exhibits the effect as a filter, thereby improving the characteristics of a noise filter.

Abstract: A power factor corrected (pfc) ac-dc converter has a modified boost input and a modified buck output. Unlike the prior art boost input, the boost switch returns to the output, not to ground. Unlike the prior art buck output stage, a third switch connects to the input. This allows much of the input current to pass through the converter to the output. There is no input current measurement, but nearly ideal power factor correction is achieved through “natural modulation.” A preferred pfc ac-dc converter uses a variable dc-dc transformer on its output, as a post regulator, to provide dielectric isolation and to provide voltage level shifting. The output of the pfc ac-dc converter has the control characteristics of a buck converter, so it is a natural mate for the variable dc-dc transformer. An ac-dc buck converter is most efficient at its maximum duty cycle. It cannot regulate for a lower input voltage, but it can reduce its duty-cycle to control for higher input voltages.

Abstract: An apparatus and method for converting DC voltage across positive and negative DC buses to three phase AC voltages on first, second and third AC output lines, the method comprising the steps of providing first and second three phase inverters that include a first subset of inverter switches and a second subset of inverter switches, respectively, linking a first choke in series with the first three phase inverter between the positive and negative DC buses and the AC output lines, linking a second choke in series with the second three phase inverter between the positive and negative DC buses and the AC output lines and synchronously controlling the first and second inverter switch subsets so that switching of first and second inverter switch subsets is substantially synchronized among the three phases.

Abstract: The invention describes combination I/O modules for automation. Various combinations of inputs and output with different electrical interfaces are offered providing greater flexibility in controller hardware selection.

Abstract: In a power converter apparatus, such as an uninterruptible power supply, a phase reference signal is generated responsive to a DC voltage on a DC bus. A magnitude reference signal may be generated responsive to a phase current of an AC bus and/or the DC voltage on the DC bus. Power is transferred between the AC and DC busses responsive to the phase reference signal and the magnitude reference signal. Generation of the phase reference signal may include generating a DC voltage error signal responsive to the DC voltage on the DC bus, generating a phase offset signal responsive to the DC voltage error signal, and generating the phase reference signal responsive to the phase offset signal. Generation of the magnitude reference signal may include generating a volt-amperes reactive (VAR) error signal responsive to the phase current and generating the magnitude reference signal responsive to the VAR error signal.

Abstract: An inverter control circuit with a resonant frequency modulation function provides a control circuit module that can modulate different resonant frequencies externally to fit loads of different modes without changing the inverter components such as a voltage transformer or redesigning the circuit layout. The RC oscillation circuit of a resonant frequency controller of the invention includes several separate resistors, and the separate resistors of the RC oscillation circuit are coupled to at least one switcher to form an open circuit or a closed circuit to determine the total resistance of the RC oscillation circuit for modulating different resonant frequencies.

Abstract: The present invention relates to a power converter for supply of electrical power to an aircraft on the ground. More specifically it relates to a power converter comprising a housing enclosing a frequency converter for provision of a stabilized multi-phase alternating output voltage to an aircraft through an output cable that is supplied from a cable drum integrated in the housing and facilitating connection to aircrafts with variable distances between their power sockets and the converter.

Abstract: The invention relates to a circuit arrangement for producing an alternating voltage or an alternating current from a unipolar direct current source having an inverter relating to a neutral conductor. The direct current source is connected to an inverter which converts the unipolar voltage of the direct current source into a bipolar intermediate circuit voltage that is stored in a buffer circuit (C1, C2) which is connected to the inverter. The inverter comprises a clocked switch (So) and an energy converting unit which is configured as a dual coil (DR1,DR2) having two windings (W1,W2) which are closely coupled to each other.

Abstract: Described herein are systems, methods and apparatuses for providing power to an irrigation controller. In one implementation, an apparatus comprises an alternating current (AC) to direct current (DC) voltage converter configured to convert an input AC voltage into a DC voltage. An AC voltage generator is coupled to the AC to DC voltage converter, wherein the AC voltage generator is configured to generate an output AC voltage using the DC voltage. The AC voltage generator is further coupled to the irrigation controller, and the AC voltage generator is configured to supply the output AC voltage to the irrigation controller.

Abstract: A method and apparatus for converting X phase intermediate voltages on X intermediate lines to output voltage for driving a single three phase load, the apparatus comprising a positive DC bus, a negative DC bus and first and second three phase drives that each include a rectifier section and an inverter section, the rectifier sections each linked to a separate three of the X intermediate lines and to the positive and negative DC buses and the inverter linked to each of the positive and negative DC buses and to the single phase load such that each of the drives has a common positive DC bus and a common negative DC bus.

Abstract: A power converter for coupling an electrical machine to an electrical grid includes a machine side converter and a grid side converter, each, side having a plurality of corresponding stages for converting a three-phase electrical signal of the electrical machine to a three-phase electrical signal of the electrical grid. The machine side converter includes a plurality of single-phase bridges coupled in series. The grid side converter includes a plurality of three-phase bridges. Each three-phase bridge corresponds to one of the single-phase bridges of the machine side converter. Each three-phase bridge is coupled to the primary windings of a corresponding transformer. The secondary windings of each corresponding transformer is phase-shifted from its primary windings and is coupled to secondary windings of another respective transformer, thus providing for coupling of the three-phase bridges in a series.

Abstract: An apparatus and method for supplying a direct current power source capable of compensating a power factor of an input power source by increasing and decreasing energy required by load changes, the apparatus comprising: an input current detecting unit for detecting an input current amount to determine a load size, a switching control unit for outputting a switching control signal to compensate a power factor of an input power source based upon the determined load size, a filtering/rectifying unit for reducing a harmonic of the input current and rectifying an input AC voltage, a power factor compensating unit for supplying charged energy to the load based upon the switching control signal, a smoothing unit for smoothing the rectified input AC voltage into a DC voltage, and an inverter for converting the smoothed DC voltage into an AC voltage and outputting the converted AC voltage to drive the load, whereby the power factor compensation (PFC) standard can be satisfied although the load is increased, and a fabr

Abstract: A vehicle includes an engine, a controller for turning off the engine when the vehicle is idle, a motor/generator for starting the engine, an inverter for converting a DC auxiliary voltage from a battery into an AC voltage for powering the motor/generator, and a device for isolating a DC voltage from the DC auxiliary voltage to prevent voltage sag in a vehicle system during engine starting. The device includes a transformer, a rectifier/regulator, and an isolator. A mechanical relay opens, or an FET is activated, to isolate the DC voltage during engine start. A method for preventing voltage sag in an auxiliary vehicle system includes detecting a commanded engine start, comparing a measured auxiliary voltage to a threshold, isolating a predetermined DC voltage from a DC auxiliary voltage when the measured auxiliary voltage is less than the threshold, and powering the auxiliary vehicle system using the isolated DC voltage.