GB2034985A

GB2034985A - An electrical machine

Info

Publication number: GB2034985A
Application number: GB7840172A
Authority: GB
Original assignee: Thyssen Industrie AG
Current assignee: ThyssenKrupp Technologies AG
Priority date: 1978-10-11
Filing date: 1978-10-11
Publication date: 1980-06-11
Also published as: GB2034985B

Abstract

An electrical machine comprises a rotor (1), a multi-phase stator (4), (5) and a converter (10 10') combined structurally with the stator such that the main stator winding contacts (9) may easily be connected to the terminals of the converter and operative to vary the number of phases of the stator winding while the frequency and/or amplitude of the winding voltage is kept constant or varied. The converter may comprise thyristors ignited at fixed times in a fixed sequence by a control device (12) and extinguished by natural commutation, or cam operated switch contacts. The machine may be operated in the generator mode in which the frequency and amplitude of the voltage output may be varied while the speed of rotation remains constant, or the motor mode in which the speed of rotation may be varied while the frequency and amplitude of the mains voltage remains constant. The machine is suitable as a diesel-electric locomotive generator or for rolling mill drives and conveyors generally. <IMAGE>

Description

SPECIFICATION An electrical machine The invention relates to an electrical machine with a rotor, a stator with multi-phase winding and a convertor device changing over to a different number of phases, with constant or variable frequency and/or amplitude.

Variable speed devices with A.C. motors are required for manifold purposes. To make it possible to effect the change of speed with small power losses, it is necessary for the motors to be supplied with alternating current of variable frequency and variable voltage amplitude. This can be carried out with the aid of rotary converters or static transverters.

A particular case of such drives is that of dieselelectric locomotives with A.C. traction motors, in which it is necessary to be able to run the motors over a wide range of speeds with constant traction, that is constant efficiency. To make this possible the A.C. traction motors must be supplied with power at variable frequency and variable voltage. There must be no direct relationship between the speed of the traction motors and the speed of the diesel engine, so that the speed of the diesel engine can be adjusted to the requirements of optimum overall efficiency, or in accordance with other over-riding considerations (noise, exhaust).

In the case of diesel-electric locomotives with A.C.

traction motors, it is a familiar practice, in order to fulfil these requirements, in the first place to rectify the constant 3-phase voltage produced by the main generator (intermediate D.C. circuit) and then to convert the current by means of a static transverter with positive commutation, to a 3-phase voltage variable in frequency and/or amplitude, which is then available for supplying the traction motors.

This technique is expensive; the components required for this purpose, viz: a rectifier with an intermediate D.C. circuit (with ancillary condenser and smoothing choke) transverter with commutation devices are heavy and need a great deal of space.

In the case of another familiar electrical machine (German Patent Specification No. 1 960 162) the production of a variable speed at constant frequency is achieved by the use of a rotating, independently driven set of brushes, connected to slip rings, which operates in conjunction with a stationary commutator, connected to a stator winding. The set of brushes rotate around the rotor with a fixed difference in speed, as a result of which a rotating field is generated in the stator with a frequency of rotation which can be controlled and which rotates with the desired speed and in the desired direction. As a result of the continual relative movement between the rotating brush holder and the stationary commutator, this design is very subject to wear.In addition considerable disturbing forces resulting from centrifugal force affect the rotating set of brushes, and interfere with the commutation process.

The purpose of the invention is to provide an electrical machine, new in principle and in design, to a large extent free from wear, which whilst simple to make is versatile in use and easily adaptable to varying conditions, such as for instance the number of phases.

This problem is solved in accordance with the invention by means of an electrical machine of the type initially described, as a result of the converter device being structurally combined with the machine, which can function alternatively as a generator with variable frequency and variable voltage amplitude, the speed remaining essentially constant, or as a variable-speed motor with constant frequency and the amplitude of the supply mains, connected direct as a built-in component of the machine to the stator winding.

The electrical machine thus produced, which can be used either as a generator or as a motor, already contains the converter device built into the stator, and thus can be used directly in the solution of various drive problems using alternating current.

One particular field of application is that of diesel electric locomotives with 3-phase A.C. traction motors, with the electrical machine in accordance with the invention serving as the main generator producing direct 3 alternating voltages of adjustable frequency and voltage spaced at a distance of 120 from each other. This makes possible a traction drive with efficient transmission of power from the diesel engine to the driving wheels, irrespective of the ratio of loco speed to diesel speed. When braking, this electrical machine, hitherto used as the main generator, can change over to work as a motor and thus transmit the electrical power produced by the traction motors to the diesel engine, which then with the fuel supply cut off, works as an "engine brake".

Besides its use as a main generator on diesel electric locomotives with A.C. traction motors, the machine covered by the invention can also be used with advantage in other spheres in drive technology, in particular where variable speeds and/or two or four quadrant drives with high output are required (e.g. rolling mill drives, conveyor technology etc.).

The converter device built into the machine guarantees the connection of the main contacts of the machine with the ends of the stator windings in a particular time sequence. The number of phases, the frequency and the voltage amplitude, determined by the number of the stator windings, their arrangement in relation to each other, the speed of rotation of the machine and also the flux in the machine, can be changed with little loss of power by means of the converter device.

The frequency and the amplitude of the initial generator voltage can in an advantageous manner be modified with a fixed speed of rotation and constant energising from zero up to at least the phase voltage frequency or the phase voltage. As a result of this the machine is particularly suitable as a main generator for diesel electric locomotives with A.C.

traction motors.

In one convenient form the converter device comprises a number of thyristors which can be ignited at fixed times and in a fixed sequence by means of a suitable control device, and extinguished by natural commutation.

In another convenient form the converter device can, however, include an electro-mechanical control mechanism with a number of galvanic switch contacts which can be operated by cams. In the case of an electro-mechanical control mechanism the frequency of the initial voltage may in generator-mode operation exceed the frequency of the phase voltage, which is determined by speed. In motor mode operation, the maximum speed prescribed by the supply frequency can be exceeded.

An advantageous arrangement is for the cams to be arranged on a cam shaft which is driven by an auxiliary motor regulated by a control device. The control is preferably carried out as a function of the difference between the machine speed and the speed of the cam shaft. The amplitude of the initial voltage in generator-mode operation is adjustable by changing the energisation of the machine.

The machine can be driven as a whole, and also both by means of a thyristor control device and by an electro-mechanical control mechanism, preferably controlled by a motor. In the case of the thyristor control device a different valve control is necessary as between the motor and generator mode of operation, whereas the machine with a mechanical control mechanism can change over from the generator to the motor mode of operation without special measures. As already indicated, the two variants of the machine differ in their respective frequency and speed ranges, in as much as with the thyristor machine in the generator mode the frequency of the initial voltage must always be below the phase voltage (determined by speed) and in the motor mode of operation the speed of the machine cannot exceed the maximum speed prescribed by the supply frequency.These limitations do not apply however in the case of a machine equipped with a mechanical control mechanism.

The squirrel-cage rotor should be used for preference purely for motor mode operation, whereas the magnet wheel rotor should be used for combined motor and generator mode operation. The machine can be equipped with both a magnet wheel rotor and also a squirrel cage rotor. The latter should preferably be used with machines which work solely in the motor mode, whereas magnet wheel rotors should be used for preference with machines which work in the generator mode or with multi-quadrant drives.

The further advantages of the invention consist in particular in the fact that on the one hand in the generator mode of operation single or multi-phase alternating voltages with variable frequency and amplitude can be produced directly irrespective of the speed of rotation, whilst on the other hand in the motor mode the machine can be connected to an A.C. supply with a fixed frequency and voltage, whilst the machine speed can be modified with little loss of power by controlling the speed of the rotating field.

In the event of the use of the machine as the main generator on diesel-electric locmotives with A.C.

traction motors in particular, the advantages achieved by the invention consist in the factthat the components usually included between the generator and the traction motors (such as rectifier, smoothing circuit, transverter with positive commutation and smoothing chokes) can be dispensed with. The generator in accordance with the invention certainly incorporates a multi-phase machine with integrated thyristor or electro-mechanical converter equipment, and is thus bigger as a combined unit than a traditional alternator or equivalent capacity.As a result, however, ofthe simplifications arising out of the invention in pa rticular through the elimination of the intermediate D.C. circuit and the commutation functions of the transverter, and also due to the saving in smoothing equipment, the generator in accordance with the invention is considerably less expensive and also lighter and more favourable in dimensions than the technical equipment hitherto used for power transmission on diesel-electric locomotives with A.C. traction motors.

Similarly the elimination of a converter device working by means of friction contact is an advantage. The mechanical problems arising in this case from the rotating set of brushes (variations in brush-contact pressure resulting from changes in speed, alteration of the centrifugal force exerted on the individual brushes due to changes in brush weight caused by wear) give rise to considerable commutation problems as well as a undesirably high degree of wear on the converter device.

The design of the converter device with stationary semi-conductor or contact control elements and the integration of the converter device with the electrical machine as a built-in integral part thereof ensures commutation with little or no maintenance and a high degree of compactness.

Examples of the invention are described below with reference to the drawings.

Fig. 1 shows a diagrammatic cross section of the machine with a thyristor converter device, Fig. 2 shows a cross section with an electromechanical converter device, Fig. 3 shows the circuit diagram of the stator windings and the thyristor valves of the converter device, Fig. 4 shows the circuit diagram of the stator windings and the contact units of the electro-mechanical converter device, Fig. 5 shows the voltage curves u = f (t) of the machine with a thyristor converter device in the generator mode, Fig. 6 shows the voltage curves of the machine with an electro-mechanical converter device in the generator mode, Fig. 7 shows the voltage curves of the machine with a thyristor converter device in the motor mode.

The electrical machine in accordance with Figs. t to 4 is designed as a 3-phase machine with an independently energised magnet wheel rotor. The rotor 1 is fixed to the shaft 2 and is independently energised via the slip rings 3. The stator 4 with the 12-phase stator winding 5 is fixed into the machine casing 6.

The bearings 7 for the shaft 2 are housed in two bearing brackets 8, which are connected to the cas ing 6. The right-hand bearing bracket is provided with special openings or gaps which make possible the connection of the ends of the windings 9 with the converter device 10 or 10' arranged in the casing 6.

In Fig. 1 the converter device consists essentially of thyristors. The converter device also incorporates cooling units which may conveniently be cooled by a ventilator 11 fixed to the machine shaft 2. The ignition of the thyristors is effected from a control unit which in Fig. 1 is shown arranged away from the machine. The main electrical connections of the machine are marked R, S, T.

In accordance with Fig. 2 the converter device 10' is constructed from a number of galvanic switch contacts which can be operated by a cam arrangement or a cam and cam follower system. The cam shaft is driven via an auxiliary motor 13, the speed of which again can be controlled by a pre-set device. Fig. 2 also shows a design in which the adjustable unit is also arranged outside the machine, although this is not always necessarily the case. The construction of the converter device mechanism is generally familiar and therefore does not need to be discussed in greater detail.

Fig. 3 shows the connections of a 3-phase machine in accordance with the invention with a 12-phase stator winding and a thyristor converter device. Any necessary protection or commutation connections of the thyristors (T1.1.R . . . T12.2.T) are not shown.

The connections of the same machine, but provided with electro-mechanical contact units (K1.R . . .

K12.T) is shown in Fig. 4 similarly to Fig. 3.

The time curves for the machine voltages are shown in Fig. 5 in the case of a machine with a thyris torconverterdevice. The phase voltages (humi . . .

urn2) are a function only of the speed and of the degree to which the rotor is energised, which are here assumed to be constant. The extensively drawn out initial voltage of the machine (only one phase is shown here) results from the ignition of certain par ticularthyristors at pre-determined times by the control unit. The extinguishing of the thyristors is effected by natural commutation.

Figs. 5a . . . c show the possibility of altering the frequency and amplitude of the initial voltage whilst the speed and degree of energisation of the machine remain unchanged.

Figs. 6a .. . d show analogously to Fig. 5 the voltages of a machine with an electro-mechanical converter device. To alterthe amplitude ofthe initial voltage it is necessary here, in contrasttothethyris- tor machine shown in Fig. 5, to alter the degree of energisation of the machine. The initial frequency is controlled by the speed of the cam mechanism.

Contrary to the thyristor machine, in this case also initial frequencies can be produced which are above the frequency of the individual phase voltages (Fig.

6d). The latter is conveniently achieved by reversing the direction of rotation of the cam shaft.

Fig. 7 shows the curve of the machine voltages for a 3-phase thyristor machine in the motor mode of operation. In this case urni... um,2 show that phase voltages of the machine and UR, US, UT show the voi- tages of the A.C. supply. The drawn out segments of the curves show the valves in ignited condition. As the ignition of the valves takes place only in the lower part of the mains voltage, it is possible to control the valve current also the total current absorbed by the machine continuously and independently of the motor speed.

Claims

1. An electrical machine with a rotor, a stator provided with a multi-phase winding and a converter device changing to another number of phases whilst the frequency and/or amplitude remain constant or are varied, characterised by the converter device being structurally combined with the machine which can be operated alternatively as a generator with variable frequency and variable voltage amplitude with the speed of rotation remaining essentially unchanged, or as a motor with a variable speed whilst the frequency and amplitude remain constant at those of the supply mains, and being connected as an integral component direct to the stator winding.

2. A machine in accordance with Claim 1 characterised by the frequency and also the amplitude of the initial generator voltage at constant speed and constant excitation from zero at least up to the phase voltage frequency or the phase voltage respectively.

3. A machine in accordance with Claim 1 characterised by the rotor being either a magnet wheel or squirrel cage rotor.

4. A machine in accordance with one of the above claims, characterised by the converter device comprising a number of thyristors capable of being ignited at specific times and in a pre-determined sequence by means of a control device and extinguished by natural commutation.

5. A machine in accordance with one of the claims 1 to 3, characterised by the converter device comprising an electro-mechanical control mechanism with a number of galvanic switch contacts capable of operation by means of cams.

6. A machine in accordance with claim 5, characterised by the cams being arranged on a cam shaft which can be driven by an auxiliary motor regulated by a control device.

7. A machine in accordance with claims 5 or 6, characterised by the control being effected as a function of the difference between the machine speed and the cam shaft speed.

8. A machine in accordance with one of claims 5 to 7, characterised by the amplitude of the initial voltage in the generator mode being adjustable by modification of the degree to which the machine is energised.

9. A machine in accordance with claim 4, characterised by the motor current in the motor mode being controllable within figures as small as desired, irrespective of the motor speed.

10. An electric rotativefield machine substantially as hereinbefore described with reference to any one of the Figures of the accompanying drawings.

10. An electrical machine substantially as hereinbefore described with reference to any one of the figures of the accompanying drawings.

New claims or amendments to claims filed on 10 Dec 1979.

1. An electric rotating field machine comprising a rotor, a stator provided with a multi-phase winding, a commutating device which is constructionally combined with the rotating field machine and comprises a plurality of switching elements, as well as a control unit which co-operates therewith and by means of which the electric rotating field machine can be operated as a mono- or multi-phase alternating-current generator with a variable frequency and voltage amplitude and a constant rotational speed or as a mono- or multi-phase alternating-current motor with a variable rotational speed and a constant frequency and voltage amplitude of the supply system, in which the switching elements of the commutating device are respectively fixedly arranged and connected between the stator partial winding and the main connections of the rotating field machine at the supply end and in which the switching elements can be operated individually, in adaptation to the desired operating state of the rotating field machine, by the control unit at variable time intervals between consecutive switching operations and in a variable sequence.

2. A machine in accordance with Claim 1, in which the frequency and also the amplitude of the initial generator voltage at constant speed and constant excitation can be varied from zero at least up to the phase voltage frequency or the phase voltage respectively.

3. A machine in accordance with Claim 1, in which the rotor is either a magnet wheel or a squirrel cage rotor.

4. A machine in accordance with any one of the above claims in which the converter device comprises a number of thyristors capable of being ignited at specific times and in a pre-determined sequence by means of a control device and exting uished by natural commutation.

5. A machine in accordance with any one of the claims 1 to 3 in which the converter device com prises an electro-mechanical control mechanism with a number of galvanic switch contacts capable of operation by means of cams.

6. A machine in accordance with claim 5 in which the cams are arranged on a cam shaft which can be driven by an auxiliary motor regulated by a control device.

7. A machine in accordance with claim 5 or claim 6, in which the control is effected as a function of the difference between the machine speed and the cam shaft speed.

8. A machine in accordance with any one of claims 5 to 7, in which the amplitude of the initial voltage in the generator mode is adjustable by modification of the degree to which the machine is energised.

9. A machine in accordance with claim 4 in which the motor current in the motor mode is controllable within figures as small as desired, irrespective of the motor speed.