Abstract: A method of and a system for controlling a permanent magnet AC generator (10), wherein the generator is provided with stator windings and permanent magnets in the rotor and wherein the generator is connected to a drive unit (50), wherein the generator is further provided with a semiconductor converter provided with AC output connected to the generator output and a DC link for controlling the output voltage of the generator, and the converter is further provided with filter means for filtering the output of the converter so that a filtered output of the converter is fed to the generator output.

Abstract: A generator control unit for fast field discharge of a field coil is disclosed. The generator control unit comprises a control domain for detecting an excessive generator output voltage, a buck regulator with a feedback pin fed from the control domain, and an over-voltage protection switch connected in a field coil return path which is bypassed by a voltage limiting device. The control domain receives a point of regulation voltage feedback and upon detection of an over-voltage, emits a disable signal to cause the buck switch shut off along with the over-voltage protection switch. Thus dual breaking points are created at two ends of the field coil to dissipate the field charge quickly through the voltage limiting device. When the buck switch experiences a shorting failure, the over-voltage protection switch provides a second breaking point to allow the field discharge through the voltage limiting device, thereby controlling the field discharge with directly controlled over-voltage protection switch.

Abstract: In an electrical power system of a diesel powered system having at least one diesel-fueled power generation unit, the electrical power system configurable in a starting mode for cranking the diesel fueled power unit, the electrical power system having a synchronous machine coupled to the diesel-fueled power generation unit, the synchronous machine having a field winding connected in a parallel relationship with a current conditioner, a method for reconfiguring a baseline circuit topology of the electrical power system for controlling a voltage being developed across the field winding including uncoupling the field winding from the parallel relationship with the current conditioner, and coupling the field winding in a series relationship with the current conditioner.

Abstract: A rotary electric machine for a vehicle includes a rotor, a stator and a rectifying device for current AC/DC conversion. The machine operates as a motor and a generator. The machine includes a multi-phase windings, switching elements forming a rectifying device, and a controller for controlling a current path of the multi-phase windings by switching the switching elements on and off to perform two modes of operation. The switching elements are switched such that one end of each windings is connected to either a high electrical potential end or a low electrical potential end of the rectifying device and the other ends of the windings connected together to be the same electrical potential are connected to either the high electrical potential end or the low electrical potential end in the rectifying device.

Abstract: Methods for increasing a total reactive power capability of a cluster of wind turbines operationally connected to a grid and systems for carrying out the methods. The method includes generating a voltage value representative of a grid voltage level, determining a total required reactive power value based on the voltage value, and activating at least one wind turbine in said cluster to increase the total reactive power capability from a present value to the required total reactive power value by a predetermined amount.

Abstract: It is an object to supply, to the utmost extent, reactive power according to a demand of a utility grid side while maintaining the power factor within a predetermined range. The wind turbine generator system includes a main controller 19. The controller 19 includes a first controller 31 performing constant-reactive-power regulation, a second controller 32 performing constant-power-factor regulation, a judging unit 34 for judging whether a present operating condition is within a predetermined operating region, and a control-switching unit 35 for switching from the first controller 31 to the second controller 32 when the first controller 31 is performing the constant-reactive-power regulation and the judging unit 34 detects a deviation from the operating region.

Abstract: An apparatus and method for allowing continuous operation of a generator control unit (GCU) despite a ground fault short circuit is disclosed. More specifically, a generator control unit (GCU) that maintains an isolated power pass domain in a completely floating set up with respect to the ground referenced control domain is used to allow continuous operation of a generator control unit (GCU) even when an internal wiring such as a permanent magnet generator wire or a generator field coil wire comes in contact with the chassis due to failure of the insulation. In addition, the apparatus and method also utilizes a high ohmic resistor as the only connection between the isolated power pass domain and the ground referenced control domain to control the voltage spike that occurs during a ground fault short circuit.

Abstract: A frequency converter circuit for a double-fed asynchronous generator with a variable power output, which can be connected to a voltage network contains a rotor rectifier, which can be connected to the rotor of the asynchronous generator, a network frequency converter, which can be connected to the voltage network, and an intermediate circuit. The intermediate circuit contains a semiconductor switch arranged on the rotor rectifier, an intermediate circuit capacitor arranged on the network frequency converter, and a diode arranged between the semiconductor switch and the intermediate circuit capacitor. According to a method for operating such a frequency converter circuit, the semiconductor switch is kept closed during the sub-synchronous operation of the asynchronous generator, and during at least some periods of synchronous or super-synchronous operation of the asynchronous generator the semiconductor switch is opened.

Abstract: A power generation system includes a rotary power generator for generating a variable-frequency alternating current, a generator side converter for converting the variable-frequency alternating current into a DC current, a DC link coupled to the generator side converter for receiving the DC current, a line side converter coupled to the DC link for converting the DC current into an alternating current with controlled amplitude or frequency, a generator side controller for receiving a DC link voltage command signal and a DC link voltage feedback signal and generating control signals for the generator side converter, and a line side controller for receiving a generator torque command signal and a generator torque feedback signal and generating control signals for the line side converter.

Abstract: A control system for an electrical power generation system (EPGS) provides overload protection without disconnecting a generator of the EPGS from an excessive electrical load. Available engine power and current levels of the electrical load are continuously measured. A command voltage is calculated that corresponds to a voltage required to sustain with the maximum available power. Output voltage of a generator of the EPGS is controlled at the calculated command voltage so that a power limit of the engine is not exceeded during electrical overload conditions.

Abstract: A system for controlling torque ripple in a permanent magnet synchronous machine includes a power converter configured to be coupled to the permanent magnet synchronous machine and to receive converter control signals and a system controller coupled to the power converter. The system controller includes a fundamental current controller configured for providing fundamental voltage commands, a harmonic current controller configured for using harmonic current commands, current feedback signals from the permanent magnet machine, and fundamental current commands in combination with positive and negative sequence regulators to obtain harmonic voltage commands, and summation elements configured for adding the fundamental voltage commands and the harmonic voltage commands to obtain the converter control signals.

Abstract: A power distribution system is provided for supplying power to a variable speed motor for rotating a shaft. The system comprises a variable speed prime mover adapted to generate an A/C output having a variable frequency corresponding to the speed of the prime mover, a power switch, a power distribution bus connected to the A/C output of the prime mover and connected, via the switch, to the motor such that the motor's speed is varied relative to the frequency of the A/C output, and a variable frequency drive operatively connected to the A/C output of the prime mover via the bus and effective to provide an alternate A/C output to the motor after the motor is disconnected from the bus. The switch is adapted to disconnect the motor from the bus when the prime mover's speed is equal to or within a predetermined range of the prime mover's speed limit.

Abstract: Disclosed is a pole count changing generator capable of altering the number of poles contained within a generator. This pole count change is accomplished by changing the path through which electrical current is capable of traveling in response to a control signal sent to a pole count changing circuit.

Abstract: An apparatus includes a vehicular electric power generation system comprising a variable speed internal combustion engine, a first variable speed electric power generator driven by the engine, a second variable speed electric power generator driven by the engine, a first inverter to receive electric power from the first generator a provide a first controlled electric output, a second inverter to receive electric power from the second generator and provide a second controlled electric output, and a controller coupled to the engine. The controller is responsive to variation in electrical loading of the first inverter and the second inverter and a degree of electrical load imbalance between the first inverter and second inverter to provide one or more engine control signals. The engine is responsive to the one more engine control signals to change rotational operating speed to adjust for the variation in electrical loading and the degree of electrical load imbalance.

Abstract: An apparatus for generating power in an enclosure includes a power generation device configured to operate in the environmental conditions of the enclosure, a first power storage device connected to the power generation device and configured to store power generated by the power generation device, a power converter connected to the power storage device and configured to output power at a voltage different than that output by the power storage device, and a second power storage device connected directly or indirectly to the power converter and configured to store power output by the power converter. The second power storage device may then provide power for at least one component of an environmental monitoring system.

Abstract: An integrated fault and personnel protection system and method for a multi-thread converter in a wind turbine power system is provided. The structure and method provide for system optimization, as well as, arc flash protection. Fault sensing with means of removing power applied to the converter minimizes the energy available to produce an arc flash event. Sensing and disconnects devices for the protections are provided close to the source of energy to protect more of the system. Converter controls detect, identify and isolate faults selecting the best combinations of the novel specific fault isolation devices. Components are distributed into separate physical to enhance protection.

Abstract: A system and method are provided to isolate outputs of parallel converter threads of a power system converter of a wind turbine generator by utilizing isolated power windings on the output transformer from the converter. Such isolation eliminates the circulating common mode current between the parallel converters of the wind turbine system and eliminates the need for a common mode inductor. System reliability is enhanced and total system cost is reduced.

Abstract: A system and method are provided to isolate outputs of parallel converter threads of a power system converter on a generator side of a wind turbine generator by utilizing isolated power windings on the wind turbine generator. Such isolation eliminates the circulating common mode current between the parallel converters of the wind turbine system and eliminates the need for a common mode inductor. System reliability is enhanced and total system cost is reduced.

Abstract: A power generation control apparatus of a rotating electrical machine for a vehicle is obtained which achieves load response control in a plurality of electric power generation control modes even if a generation voltage final target value rapidly changes. The apparatus includes a power control unit 103 and a storage battery 104 connected to a rotating electrical machine 102, and a rotation speed detection part 105 for detecting a rotational speed Na. The power control unit 103 controls power generation in a first mode when the rotational speed Na during operating as a generator is less than or equal to a predetermined value, and controls power generation in a second mode when the rotational speed Na is higher than the predetermined value.

Abstract: An electric power generation control apparatus for a vehicle alternator mounted on a motor vehicle performs one of a constant output voltage control a constant torque control and a constant exciting current control in order to suppress a hunting phenomenon of the vehicle alternator. First of all, the electric power generation control apparatus performs the constant output voltage control when a rotation speed is within an idling rotation speed range or a periodic change of the rotation speed is not less than a predetermined value. After completion of the constant output voltage control, when judging that the idle hunting phenomenon is not adequately suppressed, the electric power generation control apparatus performs one of the constant torque control and the constant exciting current control.

Abstract: An apparatus for producing hydrogen having compressor motor speed control. The apparatus includes a hydrogen generator for producing a product comprising hydrogen and a compression unit for compressing the product. The hydrogen generator can include a fuel processor having an oxidizer and a reformer. The compression unit has an induction motor and means for regulating the speed of the motor. The means for regulating the speed of the motor can include a variable frequency drive or soft start device having a plurality of switches and an adjustable ramp timer. A downstream unit including one or more of a purification unit, a second compression unit, and a storage unit is disposed downstream of the compression unit. A method for producing hydrogen is provided that includes generating a product comprising hydrogen in a hydrogen generator, compressing the product in a compression unit having an induction motor and regulating the speed of the motor in response to transient operations of the hydrogen generator.

Abstract: A method of and a system for controlling a permanent magnet AC generator (10), wherein the generator is provided with stator windings and permanent magnets in the rotor and wherein the generator is connected to a drive unit (50), wherein the generator is further provided with a semiconductor converter provided with AC output connected to the generator output and a DC link for controlling the output voltage of the generator, and the converter is further provided with filter means for filtering the output of the converter so that a filtered output of the converter is fed to the generator output.

Abstract: A generator control unit (GCU) provides active damping of a synchronous generator by monitoring the speed of the synchronous generator and detecting oscillations in the monitored speed. The oscillations are indicative of torsional oscillations within the mechanical drivetrain including the synchronous generator or generators. In response to detected oscillations in the monitored speed, the GCU generates a varying set-point value that is used to control the excitation voltage provided to the synchronous generator. Varying the excitation voltage provided to the synchronous generator causes a variation in synchronous generator torque. By selectively varying the torque in the synchronous generator, the GCU provides active damping in the synchronous generator that decreases or dampens the torsional oscillations.

Abstract: Methods and systems for reducing heat loss in a generator system are provided. The generator system includes an electrical generator and a power converter. The method includes generating electricity in the generator at a first power factor and converting electricity in the converter at a second power factor in a first mode of operation and generating electricity in the generator at a third power factor wherein the third power factor is greater than the first power factor and converting electricity in the converter at a fourth power factor wherein the fourth power factor is less than the second power factor in a second mode of operation such that the power output of the generator system in the second mode of operation is substantially equal to the power output of the generator system in the first mode of operation and the generator currents are facilitated being reduced.

Abstract: An aircraft engine power distribution system for an aircraft engine controller, such as a FADEC, is provided where the power source is independent from the conventional airframe power system, without the need for a back-up battery. The aircraft engine power distribution system includes a magnetic generator operated by an aircraft engine. The aircraft engine power distribution system also includes a power distributor that rectifies the generator output and provides the rectified power to the engine controller as its primary source of power. In this configuration, as long as the aircraft engine is able to operate the magnetic generator, the engine controller receives power. Accordingly, the engine controller operates regardless of the operational status of the airframe power system.

Abstract: A drive is embodied to drive a rotor at a variable rotational frequency; the rotor has a winding that is embodied to produce a rotary field magnetomotive force of a generator, with a rotor rotary field frequency which is variable in relation to the rotor; the frequency converter is electrically connected to the rotor winding; a regulating device comprises a recording element for measuring values of the generator, a calculating unit for a generator simulation, and a transmitter for transmitting a control signal to the frequency converter; and, on the basis of the control signal, an electrical excitation of the rotor winding can be triggered by the frequency converter in such a way that a pre-determined stator rotary field frequency is present in the event of a variable rotational frequency of the rotor and a variable rotor rotary field frequency.

Abstract: A control system for an electrical power generation system (EPGS) provides overload protection without disconnecting a generator of the EPGS from an excessive electrical load. Available engine power and current levels of the electrical load are continuously measured. A command voltage is calculated that corresponds to a voltage required to sustain with the maximum available power. Output voltage of a generator of the EPGS is controlled at the calculated command voltage so that a power limit of the engine is not exceeded during electrical overload conditions.

Abstract: A generator system is configured to supply two phase excitation current from an exciter rotor to a main generator rotor. When driven by a variable speed prime mover, the generator system provides relatively constant frequency AC power by independently controlling the main rotor flux rotational speed. The generator system includes an exciter stator that induces current in the exciter rotor windings at a desired frequency and phasing. The exciter rotor windings are electrically connected to the main rotor windings to provide two-phase excitation current to the main rotor windings. Excitation is supplied to the exciter stator from an exciter controller, which controls the frequency and phasing of the exciter excitation, based on the rotational speed of the generator, to maintain a constant output frequency.

Abstract: In an electrical power system of a diesel powered system having at least one diesel-fueled power generation unit, the electrical power system having a synchronous machine including a field winding being coupled to the diesel-fueled power generation unit, a battery for selectively providing a starting current during a starting mode of the electrical power system, and an inverter receiving the starting current for driving the synchronous machine and generating an inverter current, a circuit and method for reducing a voltage being developed across the field winding is described. The circuit includes a current conditioner for conditioning the inverter current and a parallel circuit interposed between the inverter and the current conditioner comprising a first branch including a resistance and a second branch including the field winding of the synchronous machine so that the parallel circuit is isolated from a voltage developed across the current conditioner during cranking.

Abstract: A system for controlling torque ripple in a permanent magnet synchronous machine includes a power converter configured to be coupled to the permanent magnet synchronous machine and to receive converter control signals and a system controller coupled to the power converter. The system controller includes a fundamental current controller configured for providing fundamental voltage commands, a harmonic current controller configured for using harmonic current commands, current feedback signals from the permanent magnet machine, and fundamental current commands in combination with positive and negative sequence regulators to obtain harmonic voltage commands, and summation elements configured for adding the fundamental voltage commands and the harmonic voltage commands to obtain the converter control signals.

Abstract: A thermal protecting circuit is provided for an alternator controller. The protecting circuit comprises a switching member switching on/off the alternator; a sensor sensing a temperature of the switching member; and a switching control circuit. This switching control circuit switches off the switching member when the temperature of the switching member exceeds a first predetermined temperature. This switching control circuit switches on the switching member when the temperature of the switching member is lower than a second predetermined temperature. The second predetermined temperature is set to be higher than the first predetermined temperature.

Abstract: A protection circuit for a wind turbine generator that includes a PWM Brake that works in conjunction with known Brake Relays is disclosed. The Brake Relay is used to short the generator output terminals at a first threshold voltage. The PWM Brake includes one or more switching devices, coupled across the generator output. The PWM Brake is under the control of a PWM Brake Control Circuit which actuates the PWM Brake at a second threshold voltage that is relatively lower than the first threshold voltage. In accordance with an important aspect of the invention, the PWM Brake Control Circuit includes a novel speed sensing circuit for providing a signal representative of the speed of the turbine generator The novel speed sensing circuit eliminates the need to mount a speed sensor on the pole top mounted turbine generator. As such, the need for adding cabling from the pole top mounted wind turbine generator is eliminated.

Abstract: A hand-held power tool has a drive motor driving a tool and a generator. One or more heating devices having one or more heating elements are provided. The generator supplies the one or more heating devices with energy. A control device controls a power supplied to the one or more heating elements as a function of at least one operating parameter of the drive motor.

Abstract: A generator control unit (GCU) provides active damping of a synchronous generator by monitoring the speed of the synchronous generator and detecting oscillations in the monitored speed. The oscillations are indicative of torsional oscillations within the mechanical drivetrain including the synchronous generator or generators. In response to detected oscillations in the monitored speed, the GCU generates a varying set-point value that is used to control the excitation voltage provided to the synchronous generator. Varying the excitation voltage provided to the synchronous generator causes a variation in synchronous generator torque. By selectively varying the torque in the synchronous generator, the GCU provides active damping in the synchronous generator that decreases or dampens the torsional oscillations.

Abstract: This invention discloses a power control system comprising a prime mover and a generator driven by the prime mover. A control device is coupled with the generator to ascertain a change in speed of the generator and vary an output power of the generator according to the change. The control device applies a signal to reduce the generator output power and another signal to restore the generator output power. The power control system may include a transmission, a speed converter, and/or an accessory.

Abstract: A voltage adjusting circuit prevents damage to an electrical component having no over-voltage protecting circuit when a battery is removed. An LED tail light is connected to an over-voltage protecting circuit of a CDI unit. Electric power is supplied from a power supply control section to the CDI unit and is also supplied to the LED tail light through the over-voltage protecting circuit. Thereby, the over-voltage protecting circuit of the CDI unit protects the LED tail light from an over-voltage condition.

Abstract: A power output apparatus includes first and second motor generators, first and second inverters and a relay circuit. The first and second motor generators include first and second 3-phase coils, respectively. The first inverter alters periodically the potential at a first neutral point of the 3-phase coil. The second inverter alters periodically the potential of the second neutral point of the second 3-phase coil at phase corresponding to a phase-inverted version of the potential change of the first neutral point. The relay circuit responds to a control signal from the control device to electrically connect first and second AC lines to a connector, and provides an alternating voltage generated across the first and second neutral points to the connector.

Abstract: A permanent magnet rotor of a generator is used to excite a electromagnet stator to generate electric power for the generator and to control a disengagement mechanism whereby the generator can disengage from an accessory, such as a gear box drive shaft, when the generator is not working properly. The permanent magnet is affixed to an outer ball screw which normally rotates with an inner ball screw that is operatively engaged to the accessory. An increased load to the electromagnet stator slows or stops rotation of the permanent magnet rotor and outer ball screw, causing the inner ball screw to move axially from the outer ball screw and away from an accessory and toward a re-settable lock.

Abstract: A motor drive for an electric motor receives high frequency AC current, and delivers this current through a converter which is operable to change the current delivered downstream to an inverter and an electric motor.

Abstract: In a wind power generation system, an AC input of a unit for coping with system faults is connected to an excitation converter and a DC port of the unit for coping with system faults is connected to a DC port of a converter through resistors. A plurality of energy consumptive circuits each constructed of a resistor and switching units are provided for the DC port of the unit for coping with system faults.

Abstract: The present invention provides a power converter that can be used to interface a generator (4) that provides variable voltage at variable frequency to a supply network operating at nominally fixed voltage and nominally fixed frequency and including features that allow the power converter to remain connected to the supply network and retain control during supply network fault and transient conditions. The power converter includes a generator bridge (10) electrically connected to the stator of the generator (4) and a network bridge (14). A dc link (12) is connected between the generator bridge (10) and the network bridge (14). A filter (16) having network terminals is connected between the network bridge (14) and the supply network. A first controller (18) is provided for controlling the operation of the semiconductor power switching devices of the generator bridge (14).

Abstract: A charging control apparatus is adapted to control an alternator which is operable to generate a voltage to charge a battery which is operable to supply the voltage to an electric component. An interface is connected to the alternator, the battery, and the electric component and operable to input and output a signal therebetween. A microcomputer is connected to the inter face and operable to execute a gradual change process in which a generating voltage of the alternator is gradually changed to a target generating voltage of the alternator and a sudden change process in which the generating voltage is suddenly changed to the target generating voltage. The microcomputer is operable to detect a using status of the electric component based on the signal. The microcomputer is operable to judge whether the gradual change process is required or the sudden change process is required based on the detected using status.

Abstract: An apparatus includes a vehicular electric power generation system comprising a variable speed internal combustion engine, a first variable speed electric power generator driven by the engine, a second variable speed electric power generator driven by the engine, a first inverter to receive electric power from the first generator a provide a first controlled electric output, a second inverter to receive electric power from the second generator and provide a second controlled electric output, and a controller coupled to the engine. The controller is responsive to variation in electrical loading of the first inverter and the second inverter and a degree of electrical load imbalance between the first inverter and second inverter to provide an engine control signal. The engine is responsive to the one more engine control signals to change rotational operating speed to adjust for the variation in electrical loading and the degree of electrical load imbalance.

Abstract: An aircraft starting and generating system includes a first starter/main machine assembly that includes a first exciter and a first main machine, and second starter/main machine assembly that includes a second exciter and a second main machine. The system also includes a permanent magnet generator (PMG) that is connected to the first and second starter/main machine assemblies. The system further includes a first inverter/converter/controller (ICC) that is connected to the first starter/main machine assembly and to the PMG, and a second ICC that is connected to the second starter/main machine assembly and to the PMG.

Abstract: A device for controlling vehicle power generation that controls duty cycle of an excitation winding in a vehicle power generator and controls an output voltage from the vehicle power generator to a predetermined value includes a power generation controlling circuit that, when the output voltage from the vehicle power generator is less than the predetermined value, gradually increases the value of a gradual excitation duty and gradually increases the excitation current, the gradual excitation duty being a limit value for increasing and decreasing an excitation drive duty intermittently controlling the electrification of the excitation winding, and in an opposite situation, gradually decreases a value of the excitation drive duty and gradually decreases the excitation current. The power generation controlling circuit changes the rate at which the value of the gradual excitation duty is decreased.

Abstract: A method for operating an asynchronous generator comprising receiving an indication that a power grid frequency is reduced. Responsive to the receiving the indication, reducing a speed of the asynchronous generator from a first speed to a second speed for a first time period, wherein the reduction of the speed of the asynchronous generator results in a momentary increase in a total power output of the asynchronous generator. Increasing the speed of the asynchronous generator from the second speed to a third speed responsive to the end of the first time period.

Abstract: A power converter arrangement for connecting an induction generator to an electric power network comprises a first path provided for transferring electric power from the induction generator to the electric power network during a first operation condition, and a second path provided for transferring electric power from the induction generator to the electric power network during a second operation condition, where the first path includes an AC-AC converter and the second path includes a switch. A capacitor arrangement is interconnected between the induction generator and the first and second paths and a first AC reactor device is interconnected between the capacitor arrangement and the first and second paths, where the capacitor arrangement is provided for compensating for a magnetization current of the induction generator.

Abstract: The present invention provides a power converter that can be used to interface a generator (4) that provides variable voltage at variable frequency to a supply network operating at nominally fixed voltage and nominally fixed frequency and including features that allow the power converter to remain connected to the supply network and retain control during supply network fault and transient conditions. The power converter includes a generator bridge (10) electrically connected to the stator of the generator (4) and a network bridge (14). A dc link (12) is connected between the generator bridge (10) and the network bridge (14). A filter (16) having network terminals is connected between the network bridge (14) and the supply network. A first controller (18) is provided for controlling the operation of the semiconductor power switching devices of the generator bridge (14).

Abstract: An apparatus and method for allowing continuous operation of a generator control unit (GCU) despite a ground fault short circuit is disclosed. More specifically, a generator control unit (GCU) that maintains an isolated power pass domain in a completely floating set up with respect to the ground referenced control domain is used to allow continuous operation of a generator control unit (GCU) even when an internal wiring such as a permanent magnet generator wire or a generator field coil wire comes in contact with the chassis due to failure of the insulation. In addition, the apparatus and method also utilizes a high ohmic resistor as the only connection between the isolated power pass domain and the ground referenced control domain to control the voltage spike that occurs during a ground fault short circuit.

Abstract: An electric power generating system connectable to a reconfigurable power distribution network, and wherein a number of alternators, driven by internal combustion engines running at different speeds ?1, ?2, . . . , ?n, supply alternating voltages to rectifiers (14) generating rectified voltages V(r1), V(r2), . . . , V(rn) which are maintained substantially equal.