Abstract: Hybrid-electric aircraft and a series hybrid powertrain configured to power the aircraft for a medium-haul flight. The series hybrid power train includes a plurality of energy storage units, at least one range extending generator, and a plurality of electric propulsors, each coupled to a distribution bus. The electric propulsors can produce a maximum thrust of at least 15 MW. During a cruise regime, the hybrid-electric aircraft can have an airspeed of at least 0.7 Mach at an altitude of less than 32000 feet, and the plurality of electric propulsors can have a fan pressure ratio of between 1.15 and 1.19. The hybrid-electric aircraft can have a degree of hybridization of at least 25% for the medium-haul flight and carbon dioxide equivalent (CO2e) well-to-wake greenhouse gas (GHG) emissions less than 0.25 lbs/Available Seat Mile (ASM).

Abstract: The invention relates primarily to a rotating electrical machine for a motor vehicle including: —a rotor, and—a stator (11) including a winding (17) having a plurality of phases, each phase comprising a plurality of groups of coils (G1-G4), characterized in that said stator (11) is configured such that currents in the groups of coils (G1-G4) are able to flow selectively: —in one and the same direction so as to maximize a number of poles of the rotating electrical machine, or—in opposite directions so as to minimize a number of poles of the rotating electrical machine.

Abstract: A multi-phase electric machine includes a stator core defining slots and hairpins coils disposed of in the slots and selectively joined at connections to form windings is provided. The present invention also includes a round-wide double-layer distributed winding arrangement for the multi-phase machine. The winding arrangements are winding with non-integer slots per pole per phase.

Abstract: A dynamically-reconfigurable power converter includes a controller circuit and switching circuitry. The switching circuitry includes a first set of nodes electrically connectable to terminals of an energy storage device, a second set of nodes electrically connectable to at least one winding of a rotational electric machine, and a third set of nodes electrically connectable to an external power source. Electrical measurement circuitry monitors electrical conditions at the first set of nodes and the third set of nodes. The switching circuitry is operative in a first mode to regulate power delivery from the first set of nodes to the second set of nodes, and in a second mode to regulate power delivery between the third set of nodes and the first set of nodes via the second set of nodes.

Abstract: A stator assembly, a motor, a compressor and a refrigeration device are provided. The stator assembly has a store core, tooth parts, and windings. The tooth parts are arranged on an inside wall of the stator core and distributed in a circumferential direction of the stator core. Grooves are defined between every two adjacent tooth parts. The tooth parts have a first tooth. The windings are arranged on the tooth parts by being initially wound on the first tooth and, subsequently passing through the grooves on both sides of the first tooth when being wound on other tooth parts.

Abstract: A method for controlling outputs of electric motors includes the steps of (a) providing an electric motor including a stator winding unit selected from first to fourth winding groups, each of the winding groups having at least a primary winding with a first number of poles and a first rated power, and at least a secondary winding with a second number of poles being the same as or different from the first number of poles and a second rated power being the same as or different from the first rated power; and (b) providing a control device respectively coupled with the electric motor and an external electrical power source for sensing a needed loading state of the electric motor and suppling a required connection relationship between the stator winding unit and the external electrical power source based on the needed loading state sensed by the control device.

Abstract: A propeller propulsion unit, comprising at least one kinematic system comprising at least: a heat engine, an electrical energy generator, an electric motor configured to generate a rotary movement as output from the electrical energy generated by the electrical energy generator, a drive and selection device configured to assume a first configuration, in which it is coupled to the output of the electric motor, and a second configuration, in which it is coupled to the main shaft of the heat engine, and a propeller rotated by the drive and selection device. Such a propeller propulsion unit with a hybrid engine allows more power to be provided and facilitates maintenance and ergonomics and is safer.

Abstract: An electric vehicle includes an electric motor switchable between a first mode with a first number of poles and a second mode with a second number of poles less than the first number of poles, a plurality of inverters coupled to the motor, and a control module coupled to the plurality of inverters. The control module receives current vehicle information, determines that a mode switch is required between the first and second modes of the motor based on the current vehicle information, wherein the first mode achieves higher torque than the second mode, and performs the mode switch by controlling the plurality of inverters.

Abstract: A cordless, hand-held power tool, such as a hammer drill/driver, an impact driver, an impact wrench, etc., that includes a brushless direct current (“BLDC”) motor. Each of the hand-held power tool includes a removable and rechargeable battery pack, electronics, and a BLDC motor that have been designed and balanced to produce high-performance-capable (e.g., high-power, high-current, high-torque) hand-held power tool. The hand-held power tool is capable of delivering high instantaneous (i.e., short duration) current to the BLDC motor for short-duration high power operation and high continuous (i.e., long duration) current to the BLDC motor for long duration high power operation. Additionally, the short and long duration power is capable of being provided in a smaller (in size) and lighter (in weight) power tool.

Abstract: A motor control apparatus includes: a high-pole-number controller that generates a voltage command for high-pole-number drive of an electric motor and controls operation of the electric motor under the high-pole-number drive; a low-pole-number controller that generates a voltage command for low-pole-number drive of the electric motor and controls operation of the electric motor under the low-pole-number drive; and a priority pole-number determiner that determines which one of the high-pole-number drive and the low-pole-number drive is to be given priority during switching between the high-pole-number and low-pole-number drives.

Abstract: A control device for a pole-number switching electric motor applied to a system including an electric motor capable of switching a number of poles, and an inverter electrically connected to stator windings of the electric motor; includes: a basic operation unit configured to operate the inverter to control a current amplitude which is magnitude of a current vector flowing in the stator winding, and a switching operation unit configured to operate the inverter to reduce the current amplitude before switching and increase the current amplitude after switching. The switching operation unit, the pole number switching period, operates the inverter so that a total value of the current amplitude before switching and the current amplitude after switching does not exceed a limiting current value.

Abstract: A motor device includes a stator unit including a plurality of first slots, a rotor unit rotatable relative to the stator unit, a winding unit, and a transfer switch unit. The winding unit includes first and second windings installed in the first slots. Number of poles of the first winding is less than that of the second winding. The transfer switch unit is electrically connected to the first and second windings, and is controlled to allocate access to electricity to each of the first and second windings.

Abstract: An electric motor is disclosed that includes a stator winding defining a plurality of poles, with the winding being controllable to switch between a first number of poles and a second number of poles. A rotor rotatable within the stator includes a first group of magnetic flux barriers being without permanent magnet material and a second group of magnetic flux barriers at least partially filled with a permanent magnet material. A method of operating a line-start electric motor is also disclosed.

Abstract: A pole-number-changing rotary electric machine includes: a rotary electric machine; an n-group inverter; and a control unit for controlling the n-group inverter, wherein the control unit controls current phases of a current flowing through stator coils such that a current phase degree of freedom, which is a number of current phases per pole pair controllable by the n-group inverter, is equal to a number of groups n×a number of phases m/2 at a time of high polarity driving and the number of groups n×the number of phases m at a time of low polarity driving, where the number of groups n is a multiple of 4 and the number of phases m is a natural number of 3 or more and relatively prime to the number of groups n.

Abstract: An electric machine comprising: a) a first means for providing a first magneto motive force comprising a first set of magneto motive force space harmonics comprising odd and even harmonic subsets, each harmonic in said first set of magneto motive force space harmonics having a respective amplitude, wherein one of said odd or even subsets of said first set of magneto motive force space harmonics comprises a dominant working harmonic and the other of said odd or even subsets of said first set of magneto motive force space harmonics comprises a dominant undesirable harmonic; and b) a second means for providing a second magneto motive force comprising a second set of magneto motive force space harmonics comprising odd and even harmonic subsets, each harmonic of said second set of magneto motive force space harmonics having a respective amplitude, wherein one of said odd or even subset of said second set of magneto motive force space harmonics comprises a dominant working harmonic and the other of said odd or e

Abstract: Provides a method for controlling an AC motor, including: receiving a torque command value; generating a command current based on the torque command, and a command voltage by using the generated command current in a current vector controller (CVC) current control mode; switching to a hexagon voltage manipulating controller (HVMC) voltage control mode when the command voltage enters a voltage limit area, and generating a command voltage in the HVMC voltage control mode; and controlling torque of an AC motor by using the command voltage that is generated in the CVC current control mode or the HVMC voltage control mode.

Abstract: Disclosed is a generator compressor combination power system based upon an internal combustion engine directly coupled to a generator and a compressor assembly. The engine, generator and compressor each having an operating drive shaft all positioned along the same axis, the generator is used to produce electricity and the compressor is used to compress gas.

Abstract: A stator of rotating electrical machine includes a stator core and stator coils. The stator coils have n number (where n?6) unit coils, a first coil group and a second coil group. The unit coils of the first coil group include a first unit coil located nearest the first power supply terminal. The unit coils of the first coil group include a second unit coil. The unit coils of the first coil group include a third unit coil located third nearest the first power supply terminal and adjacent to the second unit coil of the second coil group. The unit coils of the second coil group include a third unit coil located third nearest the second power supply terminal and adjacent to the second unit coil of the first coil group.

Abstract: An electrical machine comprises a rotor, and a stator magnetically coupled to the rotor and having a plurality of slots and a plurality of windings, wherein each winding is installed in a corresponding slot, a plurality of magnetic poles and a plurality of phases in each pair of poles are formed when currents flow through the windings, and the windings are so configured that the number of phases and the number of poles can be dynamically adjusted.

Abstract: A PSC/PSC motor for 2-pole operation and 4-pole operation. The motor uses an independent 2-pole main winding and an independent 4-pole main winding. An auxiliary winding includes an independent 2-pole auxiliary winding, an independent 4-pole auxiliary winding, and a shared auxiliary winding used in both the 2-pole operation and the 4-pole operation.

Abstract: A ram air fan control system includes a ram air fan motor, the ram air fan motor being a pole-change induction motor with at least two pole-count configurations, a ram air fan contactor in operative communication with a first pole-count configuration of the ram air fan motor over a ram air fan conductor bus, a ram air fan power controller in operative communication with the ram air fan contactor, a common contactor in operative communication a second pole-count configuration of the ram air fan motor over a common conductor bus, the common conductor bus being separate and electrically isolated from the ram air fan conductor bus, and a common power controller in operative communication with the common contactor.

Abstract: A ram air fan control system includes a ram air fan motor, the ram air fan motor being a pole-change induction motor with at least two pole-count configurations, a ram air fan contactor in operative communication with a first pole-count configuration of the ram air fan motor over a ram air fan conductor bus, a ram air fan power controller in operative communication with the ram air fan contactor, a common contactor in operative communication a second pole-count configuration of the ram air fan motor over a common conductor bus, the common conductor bus being separate and electrically isolated from the ram air fan conductor bus, and a common power controller in operative communication with the common contactor.

Abstract: A PSC motor includes a stator core, a rotor arranged in a rotation relationship with respect to the stator core, a first to eighth winding coil sets wound around the stator core and a capacitor. The motor has two kinds of configurations for 4-pole and 6-pole operation modes, respectively. Both configurations comprise a primary winding and a secondary winding which is connected in series with the capacitor, and have two reversible operation directions. The configurations operate different sets of winding coils when operating in different directions.

Abstract: A three-phase, multi-speed electric induction motor assembly is configured to include a controller to change motor speeds. The motor assembly includes a stator core assembly, a pair of main winding coil groups corresponding with each phase, and a pair of selectable extra winding coil groups corresponding with each phase. During the lower-speed operation, the controller connects a first set of three leads to a power source such that only the main coil groups are energized. During the higher-speed operation, the controller connects a second set of three leads to the power source such that both the main coil groups and the selectable extra coil groups are energized.

Abstract: The present invention relates to a self-propelled working machine, especially in the form of a surface milling machine, such as asphalt-milling machine or snow-milling machine comprising a main operating unit and/or a drive unit, which is operable in a steady-state or near steady-state operating status and is drivable by a drive device comprising at least an electrical motor, the electrical motor being associated with a start-up including a frequency converter for the limitation of starting current. The invention also relates to a process for operating such a self-propelled working machine. According to the invention an operating circuit for steady-state operation is provided, comprising a jumper for bridging the frequency converter following starting or reaching steady-state operational status. Optionally, the jumper is switchable to activate or inactivate the frequency converter of the start-up circuit, respectively.

Abstract: A multiple-winding induction machine may be used to obtain a reduced-speed-variation electric drive when using a variable-frequency power distribution system. Each winding may have a different number of poles. The winding with the smallest number of poles may operate the machine at the lowest bus frequency, while the winding with the largest number of poles may operate the machine at the highest bus frequency. In one embodiment, a third winding, with a middle number of poles, may operate the machine at the middle frequency ranges. The speed of the induction machine is a function of the electrical frequency and the number of the winding poles. Therefore, the operating speed range can be reduced by switching from one winding to another. According to the present invention, windings with different numbers of poles can be designed to achieve different reductions in speed variation.

Abstract: Disclosed are a driving circuit for a single-phase SRM and a driving method thereof. The driving circuit for the single-phase SRM includes a switched reluctance motor, a voltage source which supplies energy to the switched reluctance motor, and an inverter circuit which is connected to the switched reluctance motor in parallel so as to temporarily store energy of the voltage source, and then supply the energy to the switched reluctance motor.

Abstract: A variable speed motor includes a main winding including first and second main windings, and an auxiliary winding including first and second auxiliary windings, wherein the main winding and the auxiliary winding are wound on a stator to form a plurality of poles, and a plurality of relays for performing a switching operation between serial/parallel connections of the first and second main windings or the first and second auxiliary windings. The variable speed motor includes a stator on which a 4-pole winding and a 12-pole winding arc wound, a plurality of tap windings connected in series to a 4-pole main winding forming 4 poles, for extending a variable range of rotation speed of the motor during a 4-pole operation mode, and a phase control circuit for varying rotation speed of the motor by controlling a phase of an input power-supply signal during a 12-pole operation mode.

Abstract: A power tool having an electronically commutated DC motor capable of providing various operating modes ranging from a maximum efficiency operating mode to a maximum power operating mode. The motor has a rotor having permanent magnets mounted in recesses in a back iron of the rotor. In one embodiment the motor has three phase windings, each having at least a pair of coils. The phase windings are connected in either a delta or a wye configuration via electromechanical or electronic switching components, or a combination of both, by a controller within the tool. The coils in each phase winding can also be switched between series and parallel configurations to configure the motor to provide its various operating modes. In one embodiment a dual wound motor is disclosed that has its phase coils dynamically or statically switchable between series and parallel configurations.

Abstract: A system, method and article for detecting a polarity of a rotor in a motor and/or a generator. In one embodiment, a rotor polarity detection signal is applied and a response thereto is evaluated to determine whether an estimated position of the rotor is correct.

Abstract: A method for selectively operating an electric motor in one of a first pole configuration and a second pole configuration is provided. The first pole configuration has a first phase winding structure, a second phase winding structure and a third phase winding structure. The method includes energizing each of the first phase winding structure, the second phase winding structure and the third phase winding structure to operate the electric motor in the first pole configuration. The first phase winding structure is reconfigured to form a first phase, a second phase and a third phase of the second pole configuration. The first phase winding structure is energized and each of the second phase winding structure and the third phase winding structure is de-energized to operate the electric motor in the second pole configuration.

Abstract: In a method of estimating a magnetic pole position in a synchronous motor, an alternating current voltage having ?- and ?-axes components in an ?? coordinates system representing a two-phase alternating current coordinates system is applied to the motor, and ?- and ?-axes components of an alternating current are detected from the motor. A wave height of the alternating current changing with time is approximated to a wave height not depending on time, so that a differentiated value of the wave height with respect to time is substantially set at zero. An induced voltage of the motor is calculated from the components of the alternating current voltage and the components of the alternating current. The magnetic pole position is estimated from the induced voltage.

Abstract: A permanent magnet brushless 3-phase motor comprises windings R, Y, B, each divided into a plurality of sections 1-5 and switch means S1-S12 for selectively connecting the section of the respective winding e.g. R in series and/or parallel with all other sections of that winding R. Control means are provided for actuating the switch means S1-S12 to connect the winding sections 1-5 in different configurations while the motor is running to alter the speed/torque characteristics of the motor.

Abstract: An electronic circuit for starting a single phase induction motor, of the type containing a rotor and a stator with at least one running coil (B1) and one starting coil (B2), for operating jointly with an alternating current source (F), comprising: a trigger electronic switch; a trigger circuit (TR) of said trigger electronic switch; and a blocking circuit (BL) for controlling the trigger pulses of the trigger electronic switch, said blocking circuit (BL) sustaining its blocking state while there is voltage being induced to the coils of the motor (M) by rotation of the rotor, maintaining said blocking state for a certain time after said induced voltage has been substantially reduced.

Abstract: An outer-rotor variable-speed motor, to which single-phase AC power is applied and on which a rotor is provided outside a stator, comprises first and second main windings provided on a stator of the motor to form a plurality of poles, a frequency detector for detecting the frequency of AC power applied to the motor, and a relay for connecting the first and second main windings in series if the detected frequency is 60 Hz and connecting the first and second main windings in parallel if the detected frequency is 50 Hz. The speed of the motor is kept constant even when power at different frequencies is applied, so that it is possible to reduce the manufacturing cost of the motor and reduce the power consumption, and also to reduce electromagnetic noise from the motor.

Abstract: A switch for a variable-speed induction motor includes conductive connecting pieces, a rotary member, and a driving unit. The connecting pieces are mounted in a housing, are adapted to be connected to the induction motor, and have distal contact parts that surround an axis of the housing. The distal contact parts of any two of the connecting pieces form either an angular or height difference therebetween with respect to the axis. The rotary member is rotatable about the axis inside the housing, and is formed with contacting regions that are arranged along the axis and that are in sliding contact with the distal contact parts. The driving unit is operable so as to drive rotation of the rotary member about the axis such that the connecting pieces are bridged selectively and electrically by the contacting regions of the rotary member for varying the speed of the induction motor.

Abstract: A rotation speed search apparatus for an induction motor includes: a voltage control unit for comparing a rated current of a motor and a current detected from the motor and generating an output voltage; and a frequency control unit for comparing a reference excitation current of the motor and an excitation current detected from the motor and generating an output frequency. In case of a big load, an output frequency is reduced. Thus, the slip of the motor is moved to a slip where a maximum torque is generated to enable the induction motor to start. If the speed of the motor in operation is greater than a target frequency, an output frequency is increased, so that the motor can be operated even in the regenerative region of the motor.

Abstract: An electric motor for a motor vehicle or other machine. The motor includes a support member with electromagnets (coils) and a moving member with permanent magnets. The coils are divided into groups, each group having several sets of coils, each set having several coil units. Each coil has its own battery or other energy source. A drive circuit controls activation of the coils. At maximum power, all coils sets are energized together. At each lower power level, different groups of coil sets are operated, and a cycling circuit varies which of the groups are energized. In this way, energy drain on the batteries is evenly distributed, maximizing the operating time of the motor before recharging of the batteries is required. In one embodiment, the coils are turned on by SCRs, and transistors turn off the SCRs, providing a novel SCR turnoff circuit ideal for high voltage, low current applications.

Abstract: A coil winding number variable type motor for varying a cooling and heating capacity of a reciprocating motor includes: a plurality of coils separately wound and connected in series to each other so as to vary turn ratio among motor coils; a plurality of relays respectively connected between adjacent coils among the plurality of coils; and a relay controller for outputting and ON/OFF control signal for varying the winding number of the motor coil and controlling the relays according to a change in a load and a power supply voltage. The coil wound in the motor of the reciprocating compressor is divided into the main coil and the plurality of sub-coils and the winding number of the motor coil is varied by itself to control the stroke of the reciprocating compressor, thereby effectively coping with the change in the voltage or the load.

Abstract: A single phase, three-speed induction motor having 4, 6, and 8-pole speed configurations. In one embodiment, the motor is constructed and arranged to be used in connection with a washing machine. The 8-pole speed winding shares a portion of the 4-pole speed winding, but not all of the 4-pole speed winding is used in the 8-pole configuration. In one embodiment, the 4-pole speed winding includes four winding portions and the 8-pole speed configuration uses two of the four winding portions without the need for additional switch contacts to reconfigure the motor for operating in the 4-pole mode or the 6-pole mode. In one embodiment, shared winding portions are wound on the stator core in a generally non-sinusoidal distribution and non-shared winding portions are wound on the stator core in a generally sinusoidal distribution.

Abstract: An electric drive system is provided to generate varying amounts of output torque supplied to a driven member over a wide range of constant revolutions per minute speeds to reduce power consumption. The electric motor includes a rotor and a stator assembly. The stator assembly is disposed around the rotor and is inductively coupled to the rotor. The stator assembly further includes a plurality of poles, each pole consisting of a plurality of split windings wound so that the magnetic fluxes generated therefrom are added. Power switching circuits are provided for energizing the partition drives of split windings on each of the stator poles. A controller is used to selectively control the frequency, pulse width modulation, and partition configuration to vary the rotational speed and torque generation supplied to the driven member.

Abstract: A single phase, three-speed induction motor having 4, 6, and 8-pole speed configurations. In one embodiment, the motor is constructed and arranged to be used in connection with a washing machine. The 8-pole speed winding shares a portion of the 4-pole speed winding, but not all of the 4-pole speed winding is used in the 8-pole configuration. In one embodiment, the 4-pole speed winding includes four winding portions and the 8-pole speed configuration uses two of the four winding portions without the need for additional switch contacts to reconfigure the motor for operating in the 4-pole mode or the 6-pole mode. In one embodiment, shared winding portions are wound on the stator core in a generally non-sinusoidal distribution and non-shared winding portions are wound on the stator core in a generally sinusoidal distribution.

Abstract: The present invention provides a pole change induction motor that can obtain an arbitrary ratio between the numbers of poles and that can select an arbitrary number of turns to thereby obtain a very wide operating range and stabilize an operation when the number of poles is changed. This pole change induction motor comprises a rotor having a squirrel-cage winding, a stator having at least a set of a 2n-pole first winding and a 2m-pole second winding wound around the same stator core, a first inverter connected to the first winding, and a second inverter connected to the second winding.

Abstract: Problems associated with delta motors and motor controllers being subjected to swapped lead conditions as well as with time consuming troubleshooting are eliminated in a motor controller that automatically changes firing circuit timing for proper operation of the delta motor when it detects swapped lead condition that occurs during the installation process.

Abstract: A motor speed control circuit generates a half cycle waveform and applies the half-cycle waveform to the motor at a controlled frequency to achieve speed reduction in the motor without motor modification. The circuit includes a rectifier bridge electrically connected to a power source and the motor terminals, a polarity sensing circuit electrically connected to the power source, a frequency reducing circuit coupled to the polarity sensing circuit and a bridge enabling circuit coupled to the frequency reducing circuit and to the rectifier bridge.

Abstract: A reactor (32) and a switch (35) are interposed in parallel between U-phase, V-phase and W-phase on a power source side (31) and U, V and W terminals on a motor side (33). A changeover switch )37) is interposed between Z, X and Y terminals on the motor side (33) and the U, V and W terminals on the motor side (33). When the switch (35) is set to OFF, the changeover switch (37) is set to ON, and the switch (35) is set up so as to interconnect Z, X and Y terminals, windings of the motor are set up in the form of Y-connection, so that the motor and a power source are connected directly to each other. On the other hand, when the changeover switch (37) is switched over to OFF, and the switch (35) is set up so as to interconnect Z, X and Y terminals to the U, V and W terminals, the windings of the motor are set up in the form of &Dgr;-connection, so that the motor and the power source are connected together through the reactor (32).

Abstract: Problems associated with maintaining a large inventory of multiple types of motor controllers designed to accommodate a single motor type are eliminated in a motor controller that automatically senses if it connected to a delta motor or a wye motor and configures itself for operation in a compatible mode.

Abstract: An air compressor includes a stator, which includes an inlet and an outlet and defines a substantially cylindrical bore, and a rotor eccentrically rotatably mounted in the bore. The rotor is connected to be rotated by a three-phase asynchronous electric motor of pole amplitude modulated type which is switchable between low speed six pole operation and high speed four pole operation under the control of a controller. A pressure sensor communicates with the compressor outlet and is connected to the controller which is arranged to produce a first signal when the compressor discharge pressure falls below a first threshold value and a second signal when this pressure rises above a second threshold value.

Abstract: A speed reduction switch for a multiple speed induction motor includes a speed selector switch and a delay element. As the motor is switched from a high speed to a lower speed, the delay element temporarily prevents electrical connection of a motor auxiliary winding for low speed operation. The motor is therefore de-energized and slows down. After a preselected delay, the delay element connects the motor auxiliary winding when the motor is at a lower speed so that little magnetic braking of the motor occurs, and the motor smoothly transitions from a higher speed to a lower speed.

Abstract: The invention relates to a fan installation with at least one pole-changing asynchronous motor (6, 7) for the driving of a fan (8, 9), a regulating device (14, 15) being provided by which the speed of rotation of the asynchronous motor (6, 7) is continuously regulatable within a predeterminable speed range by reducing the voltage. The speed of rotation of the fan (8, 9) can thus be matched to the required amount of air or quantity of heat to be dissipated by only a few switchovers or switchings-on.