Abstract: A modular uninterruptible power supply is presented having multiple power modules installed therein. Each of the individual power modules contains an internal bypass circuit sized for its particular power module. Preferably internal bypass circuitry is sized to carry two per unit load. The system and method of the invention also includes internal control circuitry for each of the modular power modules that control transitions between the inverter and bypass modes of operation. This transition control is coordinated with the other controllers for the other modular power modules installed in the uninterruptible power supply. Both the high speed communication bus and a high level interrupt line are utilized to minimize the transfer break time between different modes of operation while ensuring that the inverter is never paralleled with the utility line voltage. To further minimize this transfer time, a solid state switching circuit is utilized to provide the initialization between operational modes.

Abstract: A UPS system for communications systems. The UPS system comprises an input stage that generates primary and standby AC power signals. The primary and standby AC power signals are passed through an isolation transformer and through an output rectifier to obtain an output DC power signal. A plurality of output inverters are used to generate a plurality of output AC power signals from the output DC power signal. A switch circuit is provided to connect one or more of the output DC power signals to one or more loads of the communications system.

Abstract: Aspects for sensing faults in a redundant power converter are described. An exemplary circuit aspect includes a signal transition monitor for monitoring signal transitions at a predetermined node within the redundant power converter, and a detector for detecting a fault condition in the redundant power converter when a proper signal transition fails to occur during a base period of switching. The aspects sense faults in a manner which allows replacement during a scheduled downtime, so that redundancy is restorable without having an unscheduled outage.

Abstract: A solar power generation apparatus includes solar battery arrays, each of which has solar battery modules, non-isolated inverters, each of which converts direct-current power generated by one of the solar battery arrays to alternating-current power and provides the alternating-current power to a commercial power system, an earth leakage circuit breaker arranged between the non-isolated inverters and the commercial power system and connected to outputs of the non-isolated inverters in parallel, and a controller for controlling operation of the non-isolated inverters. The controller controls start-timing of the operation of at least one inverter to be different from that of another inverter. This arrangement can prevent any undesirable operation of the earth leakage circuit breaker.

Abstract: A flat type fluorescent lamp, obtaining an improvement in efficiency of brightness and being adjustable in an emitted light amount thereof, while maintaining a uniform light emission across the surface thereof, and illuminating with no use of mercury therein, comprising a sealed container being defined between a front glass substrate and a rear glass substrate which are hermetically bonded to each other, so as to enclose a rare gas as discharge gas therein, edge electrodes, having width from 2.

Abstract: A pulse inverter with variable pulse frequency for producing a sinusoidal alternating current is provided, wherein the pulse frequency variation is dependent on the configuration of the alternating current to be produced, the pulse frequency at the passage-through-zero of the alternating current to be produced is a multiple greater than in the region of the maximum amplitude of the alternating, current and the lowest pulse frequency in the region of the maximum amplitude of the alternating current is at least 100 Hz. In a preferred embodiment, the pulse frequency in the region of the passage-through-zero of the alternating current to be produced is in the range of about 14-18 kHz, and in the region of the maximum amplitudes of the current it is about 500 Hz to 2 kHz. A wind power installation may be provided with a pulse inverter as described above, or alternatively, a plurality of wind power installations provided with pulse inverters as described above are connected in parallel relationship.

Abstract: A device for operating inverters according to the present invention can operate a plurality of inverters for converting DC output from a DC source such as a solar cell to AC output efficiently without relying on a particular inverter. The plurality of inverters are connected to the DC source through switches. DC output from a DC source is measured by a measuring device to determine the number of inverters to be operated on a basis of the output result from the measuring device. The inverters to be added or cut off are determined among the plurality of inverters at random on a basis of the random number and switches of the determined inverters are turned ON or OFF in order to select inverters to be operated.

Abstract: A multiple inverter system of the present invention is disclosed. It includes a plurality of input transformers having secondary windings and a plurality of unit inverter cells connected in series at n stages to compose respective phases and supply the electric power to a multiple phase load in combination with the input transformers. The input transformers have 3n sets of three-phase windings at the secondary side and the secondary windings of the transformers, which are out-of-phase at each phase, are connected to unit inverter cells of each phase at the n-th stages. Further, the present invention is provided with a bypass switch control to melt a fuse that is applicable to a unit inverter given with a circuit closing command by giving this circuit closing command to a bypass switch corresponding to applicable unit inverters in response to an operation abnormality detector and a DC abnormality detector.

Abstract: A power unit is provided that is not affected by a voltage fluctuation of a reverse flow-preventive diode provided in an output line thereof and that can provide a stable output controlled with a high accuracy. A first rectified diode 17 rectified and a first smoothing capacitor 18 smoothes the voltage switched by a transformer 14 to generate a DC voltage (VP) at an A point. A reverse flow-preventive diode 21 and an output resistor 22 are provided between the A point and a positive output terminal 23. The comparison/detection circuit 25 compares the anode and cathode potentials of the reverse flow-preventive diode 21 with each other. The comparison/detection circuit 25 supplies a differential amplifier 26 the anode or cathode potential whichever is lower.

Abstract: A DC to DC converter includes multiple stages to share power handling. The stages are connected in parallel paths between the source input and the load output of the power converter. An analog error signal is generated by comparing the load output signal to a reference signal. The error signal is fed to a phase shifting input of a phase lock loop. The phase lock loop is connected to receive a reference clock signal and maintain a relative clock signal shifted in phase from the reference clock signal by an amount depending on the error signal. Digital divider circuits and digital logic circuits are used to produce phase shifted variable pulse width control signals for the stages. The parallel connected power conversion stages equally share the transfer of power from the input source to an output load. A single analog to digital conversion of a single analog error signal to multiple, phase shifted, variable duty cycle clocks is provided.

Abstract: The present invention provides an uninterruptible duplexed power supply system, which is capable of achieving high efficiency and compact size, and moreover, is capable of solving for a power circuit failure in an energized state.

Abstract: A current sharing circuit scheme comprising first and second power modules (36,38) each including an input side (30) and an output side (32), the power modules (36, 38) coupled to each other via respective input sides (30), each of the output sides (32) including a positive terminal and a negative terminal. The circuit scheme also comprises first and second circuit output voltage terminals (47, 46) and first and second set point controls (40, 41) coupled to the negative terminal of each of the output sides (32). First and second initial set point controls (42,45) are included providing current signal paths between corresponding first and second set point controls (40, 41) and the first output voltage terminal (47).

Abstract: A DC voltage supply network is described for electric-motor loads, in particular on a ship. A plurality of electricity generation sets are connected in parallel on an output side, and a controllable rectifier or a DC voltage controller is connected downstream of an output of each electricity generation set and has a control input for connection of a voltage regulator. An output of the controllable rectifier or the DC voltage is coupled to an input of the voltage regulator in order to supply a voltage actual value signal and an additional signal, and is connected to the network in order to supply it. The loads are in each case connected to the network via an inverter which can be controlled via a control input by a regulator. In addition to an actual value and the nominal value, an input of the regulator is supplied with an additional signal which is derived from the inverter input voltage and/or the network voltage.

Abstract: A power supply circuit for an ion engine suitable for a spacecraft is coupled to a bus having a bus input and a bus return. The power supply circuit has a first primary winding of a first transformer. An upper inverter circuit is coupled to the bus input and the first primary winding. The power supply circuit further includes a first lower inverter circuit coupled to the bus return and the first primary winding. The second primary winding of a second transformer is coupled to the upper inverter circuit. A second lower inverter circuit is coupled to the bus return and the second primary winding.

Abstract: An inverter circuit (10) has a plurality of voltage source inverters (VSI) coupled in parallel. Each of the voltage source inverters are coupled to a load (14). A synch signal source (12) generates a square wave from a fundamental operating frequency. The square wave generated by the synch signal source (12) is coupled to each voltage source inverter (VSI). Each voltage source inverter VSI has a timer counter (22), a microprocessor (26), and an inverter (32). The timer counter (22) is preferably a triangle wave generator that corresponds to the time since a rising edge of a synch signal (18) The microprocessor (26) samples the cyclic output signal (24) and determines a phase angle for the voltage source inverter. The phase angle and the voltage magnitude are provided to the inverter (32). The inverter (32) provides an output signal to the load that has the same phase angle as the outputs of the other phase inverters.

Abstract: A device for operating inverters according to the present invention can operate a plurality of inverters for converting DC output from a DC source such as a solar cell to AC output efficiently without relying on a particular inverter. The plurality of inverters are connected to the DC source through switches. DC output from a DC source is measured by a measuring device to determine the number of inverters to be operated on a basis of the output result from the measuring device. The inverters to be added or cut off are determined among the plurality of inverters at random on a basis of the random number and switches of the determined inverters are turned ON or OFF in order to select inverters to be operated.

Abstract: A photovoltaic power generation apparatus having a plurality of power converters, respectively connected to a plurality of solar battery arrays, for converting direct-current power generated by the solar battery arrays to alternating-current power so as to provide the alternating-current power to a commercial power system. The photovoltaic power generation apparatus is so constructed that the plurality of power converters do not simultaneously suspend operation when an abnormal state is detected, in order to prevent generation of an electrical stress or reduction of the power generation amount caused by simultaneous operation suspension of the power converters or repeated operation suspension and operation resume. When the power generation amount of each solar battery array is different, a power converter connected to the solar battery array of the smallest power generation amount is set in the first-to-suspend condition.

Abstract: A power converting system has power converters for converting a direct current into an alternating current, a DC power source arranged on the DC side of the power converters, and voltage dividing transformers having windings whose first ends are connected to the power converters phase by phase and whose second ends are joined together and connected to a load phase by phase. Also provided is a controller for controlling the power converting system.

Abstract: An invertor having a plurality of invertor bridges which operate in parallel and whose output voltages are summed. The invertor bridges are driven with pulse duration modulation according to an auxiliary control voltage. The auxiliary control voltages of the individual invertor bridges have a constant phase difference between one another. The output voltages of the bridges are summed by a center tap which is grounded by a ground connection. Effective suppression of the common-mode current distortion is achieved by having the switch arranged in the ground connection.

Abstract: A multiple-wound, three-phase, variable speed motor having N independent winding sets is driven by N inverters, each responding to 1/N of the torque and excitation current commands, and the torque current is limited as a function of N times the limiting current each inverter may tolerate, when all inverters are functioning. When M inverters fail, they are disconnected from the motor, the torque current is limited as function of N-M times the limiting current each inverter may tolerate. The remaining N-M inverters may each respond to 1/(N-M) of the torque and excitation commands. The excitation current may be maximized as (N-M) times the limiting current divided by the square root of two. The speed command may be predetermined by the integration over an acceleration interval, of the maximum acceleration achievable with torque available from those of the inverters which have not failed, in view of the inverters' current limits.

Abstract: A system and method for adjusting the maximum allowable current limit for each of a plurality of parallel power supplies within an N+1 power supply system in response to dynamic variations in the total supply current capacity of the N+1 power supply system. A plurality of parallel supplies make up the N+1 power supply which provides power to a load. A sensor within each of the parallel power supplies determines an operating status of each of the parallel power supplies. A detector circuit in communication with the sensors translates the operating status determination into a supply current capacity signal. Finally, a current limit adjustment circuit generates a current limit signal in response to the supply current capacity signal, such that the maximum allowable current limit for each parallel power supply is adjusted while maintaining the overall power supply VA limit for the N+1 power supply.

Abstract: A power supply circuit for an ion engine suitable for a spacecraft has a voltage bus having input line and a return line. The power supply circuit includes a pulse width modulation circuit. A plurality of bridge inverter circuits is coupled to the bus and the pulse width modulation circuit. The pulse width modulation circuit generates operating signals having a variable duty cycle. Each bridge inverter has a primary winding and a secondary winding. Each secondary winding is coupled to a rectifier bridge. Each secondary winding is coupled in series with another of the plurality of rectifier bridges.

Abstract: The controller for a power converter of the present invention:calculates the range number in which the voltage command vector for a multi-level converter is present;rotates the voltage command vector through a specified angle;performs coordinate transformation of that vector to a vector in an oblique coordinate system which takes the vector in the a axis direction and a vector which has been rotated through a specified angle anti-clockwise from the a axis as two unit vectors;splits the converter output-enabled portion of the vector diagram of the -30 degrees +30 degrees range of the spatial vector diagram in which output vector is positioned, which has undergone oblique coordinate transformation, into square-shape patterns so that the outputs vector is positioned in the upper left/the lower right/both the lower left and upper right of each square-shape pattern;splits any square-shape pattern which holds the output vector in both its lower left and its upper right into two triangular domains by a segment which

Abstract: Universal switched power converter connected to a voltage source and, based on the level of the voltage received, this is applied to a first primary circuit comprising a first switching device (14-1) or to a second primary circuit comprising a second switching device (15-1). Control means (PWM) adapt the conducting period of the switching device connected to input terminals for regulating an output voltage and adapt the conducting period of the switching device not connected to the input terminals for demagnetising the core of a transformer (T) during the non-conducting period of the switching device connected to the input terminals.

Abstract: Methods and apparatus are disclosed for achieving load balance between parallel inverters in an AC power supply. Load balancing reduces undesirable cross conduction current between the parallel inverters. Load balancing and the resulting reduction in cross conduction current are achieved without the need for common control circuitry between the parallel inverters. Thus, the single-fault protection offered by redundant parallel inverters is not compromised by the disclosed load balancing techniques.

Abstract: A power supply apparatus in which at least one or more DC power supply devices having impedance elements with the same impedance on output lines are parallel-connected, and supply output voltages to a common load via the impedance elements includes an external adjustment voltage supply circuit for supplying an adjustable external adjustment voltage to each DC power supply device, and an internal voltage control circuit for comparing the external adjustment voltage from the external adjustment voltage supply circuit incorporated in each DC power supply device with the voltage applied to each impedance element, and controlling the output voltage so as to make these voltages equal, thereby equalizing voltages applied to the impedance elements in the respective DC power supply devices.

Abstract: The vital driver utilizes rectification and subsequent synchronized inverting of the rectified power, which is then fed to a transformer. Failed operation, which permits current having a DC component to reach the load transformer, causes an increase in the current which is sensed by a current sensor. The high current can be detected by a fuse. Some embodiments use primary modules having a rectifier section with sufficient power to run a number of secondary units, each powering an individual load. The synchronizing inverter can utilize optically coupled solid state switches.

Abstract: Buck-boost type or buck type chopper circuits and transistors are employed as inverters (IV1, IV2) and power synchronizing switches (SW1, SW2), respectively. A PWM signal is applied to transistors of the chopper circuits to convert DC voltage generated by solar cells (DC1, DC2) into positive and negative half-wave AC voltages for an AC power supply (AC1). The inverters (IV1, IV2) output the AC voltages from their AC output terminals on alternate half cycles thereby to cause backflow of power. The power synchronizing switches (SW1, SW2) performs not only the function of transmitting the half-wave AC voltages generated by the inverters (IV1, IV2) to the AC power supply (AC1) in accordance with the AC cycle of the AC power supply (AC1), but also the function of, when one of the inverters is in operation, insulating the other from the AC power supply (AC1).

Abstract: In the particular embodiments described, an unlimited voltage static power converter includes an array of multi-level phase drivers consisting of a plurality of H-bridge power modules connected in series. The midpoint node of the series-connected power semiconductors is connected to corresponding midpoint nodes in adjacent H-bridges to achieve a desired high output voltage using available power switch ratings. A three-dimensional multi-level, multi-phase, multi-circuit array of H-bridges permits the use of the static power converter for high power applications, while providing a high degree of power quality. The power semiconductor switches are operated in accordance with a two-dimensional interleaved pulse width modulation algorithm which produces a waveform with a switching frequency that can be more than an order of magnitude higher than the switching frequency of a single power switch.

Abstract: An inductive boost circuit is added in parallel with an inverter to increase current to an EL lamp. The inverter and the boost circuit each include a switching transistor. The switching transistor in the inductive boost circuit may be matched to the switching transistor in the inverter and may be driven synchronously with the switching transistor in the inverter.

Abstract: A voltage conversion device is disclosed which is to be used particularly in motor vehicles. For voltage conversion, a plurality of small voltage converters are connected as partial converters parallel to one another. By sequentially turning on the individual partial converters and superposition of the output current, a uniform output current at low input load is attained.

Abstract: A current sharing circuit has a plurality of power devices, such as diode rectifiers, connected in a parallel arrangement. Each leg of the parallel arrangement comprises one power device connected in series to an inductive element. The series resistance of the inductive element in each leg of the parallel circuit moderates the affect of temperature variations on the current drawn by each power device, which enables substantially equal current sharing to occur. As used in switch mode power supplies, such as forward converters and boost converters, the current sharing circuit provides the benefit of substantially equal current sharing between power devices without increasing resistive losses which would reduce the efficiency of the power supply.

Abstract: A high voltage inverter cascades a plurality of multiple voltage level inverter modules each fed by an isolated dc energy unit to reduce the number of stages of the inverter required to generate a desired ac voltage. Thus, where the dc energy unit includes the secondary winding of an ac transformer, the number of each winding needed is reduced. By using active rectifiers operated in a boost mode to convert the transformer secondary voltage to dc for powering the inverter modules, regenerative operation can be achieved.

Abstract: The invention relates to a power supply unit which includes an inverter having output connections whereto the primary winding of a transformer is connected via a series capacitor. The rectified secondary voltage of this transformer is applied to a use which requires a high short-time power in a first mode of operation and a lower continuous power in a second mode of operation. The maximum permissible continuous power can be increased by means of an auxiliary inductance Lh which is active in the second mode of operation but inactive in the first mode of operation.

Abstract: A multiple pulse-width modulation power conversion device for variable-speed drive of a three-phase AC motor comprises three units (11.sub.1, 11.sub.2, and 11.sub.3), each unit including n (n.gtoreq.2) batteries (12.sub.11, 12.sub.12, and 12.sub.13), each made up of a DC power supply or at least one battery cell, and n power converters (13.sub.11, 13.sub.12, and 13.sub.13) for converting the DC power of each of these batteries to single-phase AC power. Single-phase AC terminals within each unit are connected in series, and of the single-phase AC terminals within each unit, one of the single-phase AC terminals that is not connected to the single-phase AC terminal of another power converter is connected to a star connection, and the other is connected to a respective one of three input terminals of a three-phase AC motor. The power conversion device further comprises control circuits (14.sub.11, 14.sub.12, . . . , 14.sub.

Abstract: A circuit includes a plurality of DC-to-DC converter circuits and separates in time switching of the respective power switches of the DC-to-DC converter circuits which would otherwise be switching at nearly a same time, such as based upon a same desired output level. The switching time may be separated by inverting a periodic control waveform of at least one of the DC-to-DC converter circuits. The multiple output DC-to-DC converter circuit thereby provides an increased noise margin and operates with greater accuracy and stability. The circuit may also determine when the DC-to-DC converter circuits would otherwise be switching at nearly the same time, and activate the switching time separation responsive thereto. For example, the determination may be made based upon a selectable output level being within a predetermined range of at least one other output level.

Abstract: For use with a power supply including first and second parallel-coupled converters having interleaved first and second switches, respectively, the first and second switches limited to a duty cycle of less than about 50 percent, a current mode control circuit and a method of current-mode controlling the power supply. In one embodiment, the current mode control circuit, includes: (1) an interconverter current transformer, coupled to an input of the power supply, that senses an input current of the power supply and (2) a controller, coupled to the current transformer, that moderates the duty cycle of the first and second switches as a function of the input current to cause the first and second converters to share an output current of the power supply.

Abstract: A power converter circuit arrangement which comprises a first power converter and at least one further power converter is specified. The power converters are connected to the DC voltage intermediate circuit and feed a load circuit, in particular a single-phase railway grid. The or each further power converter has an output transformer on the load side. The secondary windings of the output transformers are connected in series with the primary winding of a load transformer, which feeds the load circuit, and the load-side terminals of a first power converter. This permits the turns ratios of the output transformers to be selected to be greater than or equal to one and said turns ratios between said output transformers to be selected to be gradated in a binary or ternary manner, for example.

Abstract: A partial-voltage buck regulator controls a high-voltage bus to a full-bridge circuit such that overall switching losses are reduced and distributed. Low-voltage buck regulator devices are PWM-switched when high output voltage is needed, and high-voltage bridge devices are PWM-switched when low output voltage is needed. A variable input power supply, which may be operated in a high power factor mode, can adjust the input bus voltages to achieve optimum performance for a given magnetic resonance imaging sequence.

Abstract: The present invention provides a switching power supply which operates at a high efficiency over a wide operating load range. When the output power is below a first power level, the first power converter stage operates in a hard-switching mode and the second power converter stage is off. When the output power is greater than the first power level and less than a second power level, the first power converter stage operates in a soft-switching mode and the second power converter stage is off. When an output power is greater than the second power level, the first power converter stage operates in a soft-switching mode and the second power converter stage operates in a soft-switching mode.

Abstract: A three-phase inverter for small, high speed motors such as a miniature centrifical compressor which has a low voltage, high current requirement. The inverter is supplied with DC power at 28 volts, and produces power of about 50 to 500 watts at about 15 volts, and at frequencies of about 5 to 9 kilohertz. Six D-type flip-flops with clock inputs produce twelve signals which are provided to six bridge drivers. Each bridge driver controls two MOSFET's in series. The MOSFET's are supplied with DC power. Outputs are fed to primaries of adjacent transformers in a circular array. The transformer secondaries are arranged in a star configuration to produce stepped voltage and saw-tooth current output wave forms approximating sinusoids in three phases.

Abstract: A converter system, in particular for supplying electrical drives with direct current or DC voltage, or with alternating current or AC voltage, at a specifically matched frequency or for dynamic power factor correction. The converter system has at least one converter which has power semiconductors which can be switched on and/or off. It is possible to influence the current flow through the power semiconductors by adjusting the times at which the power semiconductors are switched on and off. It is also possible to influence the desired overall voltage or the desired overall current at the output of the converter by suitably controlling the times at which the individual power semiconductors of the converter are switched on and off.

Abstract: An anode voltage of a diode for reverse current prevention provided in each power supply module is output to a current balance control terminal via a resistor. The current balance control terminals of the respective power supply modules are mutually connected, and an average level of the anode voltages in the reverse current prevention diodes of the respective power supply modules is applied to the current balance control terminals as a reference voltage level. By executing the switching control for the power MOSFET in each power supply module so as to make the anode voltage of the reverse current prevention diode in each power supply module equal to the reference voltage, the output current values of the respective power supply modules are set to be equal.

Abstract: An electrical power converter for an incoming AC transformer connected to a multiphase power source and having multiple secondary windings. Each secondary winding is connected to multiple switching cells, each of which functions like a matrix converter. The secondary windings can be either single or multi-phase and more than one transformer can be provided such that the multiple secondary windings can be distributed among individual transformers. The output of at least two of the switching cells are connected in series. The switching cells can be either bi-directional or unidirectional and can also have a three-phase input. A combination of IGBTs and diodes can form the switching cells.

Abstract: A multi-level power converter such as an inverter for changing one of a plurality of dc voltage inputs into an ac voltage output is provided which includes inverter arms disposed between dc power supplies and an ac voltage output terminal. The inverter arms include switching circuits which are selectively subjected to PWM control to establish and block communication between one of the corresponding dc power supplies and the ac voltage output terminal. The switching circuits that are not connected to either the maximum or minimum dc voltage terminal include a first switching device, a second switching device connected in series with the first switching device, a first diode connected backward in parallel to the first switching device, and a second diode connected backward in parallel to the second switching device. This structure decreases the number of floating power supplies for driving the switching elements.

Abstract: The present invention provides a multilevel electric power converter including a plurality of DC voltage sources providing different DC source voltage levels. The DC source voltage levels are preferably multiples of each other and may vary in a binary fashion or in a geometric progression with a factor of three to provide a large number of output voltage levels for a given number of inverter levels. The multilevel inverter is preferably implemented as a series connected set of H-bridge inverters, with each H-bridge inverter having an independent DC voltage source providing the desired DC source voltage level. A hybrid modulation strategy may be employed whereby the lowest voltage level inverter is modulated at a high frequency, e.g., by pulse width modulation, and higher voltage level inverters in the multilevel inverter are modulated to provide a low frequency stepped waveform. The combined high frequency pulse width modulated and low frequency stepped waveform has good spectral quality.

Abstract: In multi-phase driving systems of electric motors in a switching mode employing distinct integrated half-bridge output stages, the use of multiple external components for each integrated half-bridge stage to implement functions of adjustment of the switching dead-time and of disabling/enabling of the half-bridge stage can be avoided and an improved matching obtained by using single external components connected in common to the dedicated pins of all the distinct integrated half-bridge output stages. This is achieved by duplicating the disabling comparator, respectively for the power transistor of the pull-up branch and for the power transistor of the pull-down branch in each integrated half-bridge stage.

Abstract: An inverter having a plurality of inverter bridges which operate in parallel and whose output voltage is summed by way of a transformer. The transformer has a number of primary windings and associated secondary windings which correspond to the number of inverter bridges. Each inverter bridge is connected on the output side to a primary winding. The secondary windings are connected in series to sum the output voltages. The transformer has a center tap which is grounded by a ground connection. The suppression of in-phase or common-mode interference currents flowing by the ground connection and the interference voltages associated therewith is achieved by dividing the secondary windings into a first and second identical partial secondary winding. The partial secondary windings are connected to one another in the center tap in such a way that the common-mode currents and voltages induced in the partial secondary windings mutually cancel.

Abstract: An invertor (15) includes a plurality of invertor bridges (B1, . . . ,B8), which are connected in parallel and whose output voltages are summed via a transformer (19). The transformer (19) has a number of primary windings (P1, . . . ,P8) and associated secondary windings (S1, . . . ,S8) which corresponds to the number of invertor bridges (B1, . . . ,B8). Each invertor bridge (B1, . . . ,B8) is connected on the output side to one of the primary windings (P1, . . . ,P8), and the secondary windings (S1, . . . ,S8) are connected in series to sum the output voltages. The transformer (19) has a center tap (23) which is grounded via a ground connection (24). Tertiary windings (T1, . . . ,T8) are assigned to the primary windings (P1, . . . ,P8) and to the secondary windings (S1, . . . ,S8). The tertiary windings (T1, . . . ,T8) are also connected to a common-mode filter (51).

Abstract: A uninterruptible power system in which separate inverters are connected to separate d.c. power sources established by independent power supplies, a.c., d.c. or both, and have their a.c. outputs connected to separate transformer primary windings with the primary to secondary turns ratios of the primary windings establishing different effective secondary voltages for determining the power source for normally supplying the power from the system and the sequence in which the other power sources are used on power failure, the magnitudes of the effective voltages determining the power source for initially supplying the power with any other power source supplying the power when its effective voltage is higher than any other available power source.