DE2802753A1 - High-speed sync. motor for traction systems - has axial magnetic flux in gap between permanent magnetic rotor and two stator rings with polyphase windings - Google Patents

Abstract

The motor coilless rotor generates magnetic field by permanent magnets so that the magnetic flux permeates the motor air gap in an axial direction. The centrifugal force imparted to the rotor permanent mannets is taken up by a non-magnetic ring outside the magnets. The polyphase stator winding has salient coils with its radial conductors lying in the magnetic field. Ferromagnetic packing is used to improve permeability in the region of the magnetic field.

Description

"High-speed vehicle drive"

1. Current state of drive technology in vehicle technology Even today it is preferred to use the direct current drive. The disadvantages of the DC motors are accepted because they are compared to three-phase drives the necessary energy processing is easier. This is the case the direct current drive to a controllable or in the presence of a three-phase generator with adjustable excitation around an uncontrolled rectifier. With the three-phase drive motor however, a frequency converter is required, the cost of which is generally comparative are higher and are not compensated for by the simpler and more robust engine Various development work in recent years has shown that hopes for a simpler frequency converter with natural commutation Hard to realize if accepting concessions on the side of the three-phase machine leave, or at least lead to an overall unsatisfactory result.

If inverters with forced commutation are provided, then shows that almost every application requires a special development, which then leads to the high costs mentioned. Considerations for properties of the Semiconductor switching elements (thyristors) to be used limit the operation In many cases, the motor's clearance is undesirable. The advantages of the three-phase motor cannot be fully used because, for example, the operating voltage and cut-off frequency of the inverter do not allow this. So far there has been no type of series concept for three-phase drives, which shows the advantages of the three-phase motor convincingly brings.

2. Guidelines for the design of the vehicle drive The weight restriction on vehicles normally requires small weights and compliance with the installation dimensions for the drive.

In the case of land vehicles, there is a requirement for a low, unsprung Mass to which the drive motor makes at least a contribution.

The energy conversion losses should be low.

The motor and upstream energy processing should have a good level of efficiency to have. This is a requirement for general energy and cost reasons is raised, but also exists because there are also large losses require forced cooling, which is undesirable on vehicles.

Machines and frequency converters should be designed so that they can be used for small and large services according to simple principles, i.e. their advantages over existing solutions in a large performance range To assert itself.

There should be favorable material and manufacturing costs for the motor and actuator can be achieved. This is particularly promoted by the fact that for the inverter a modular design is used, so that the advantages of large quantities for Wear and tear and components of the same type are used regardless of the performance can.

Through the principle of several parallel units for energy processing (the inverter) should at the same time counteract the total failure of a drive motor will. Compared to previous converter concepts, increased redundancy is to be achieved will.

3. Drive motor and energy preparation 3.1 Description of the drive motor In order to design a low-loss and low-weight motor, it makes sense to use high peripheral speeds apply.

Both the related winding losses and the power per unit of the active volume are inversely proportional to the circumferential speed. One Another possibility to save losses is to use the excitation field of the synchronous machine to be generated by permanent magnets. It is assumed that today too Reasonably priced magnetic material is available that is completely demagnetized has a straight B (H) curve and induction amplitudes with air gaps of a few mm of about 0.7 T. The rapid development in the field of permanent magnets During the last few years there are further improvements or reductions in the future expect.

High peripheral speeds of the rotor require a simple rotor construction with a suitable support of the centrifugal forces. To vibration problems of the rotor to avoid and at the same time to achieve the desired simple shape appears a kind of disc shape is the cheapest solution (Fig. 1). The magnetic field occurs in the axial direction through the gap spaces. The alternating magnets support themselves more adequately against a non-magnetic ring via aluminum fittings Strength. It can, for example, consist of steel or non-magnetic steel.

Effective material utilization is achieved when the radial Expansion of the magnets is significantly smaller than the radius on which they are arranged are. A construction made of aluminum alloy, which has a hub in the center. It transfers the circumferential forces and fixes the magnets. This ensures that both the circumferential forces arising with the torque as well as the centrifugal forces of the magnets in Form of compressive forces added will. They are the only ones to generate the normal forces occurring in the axial direction in tensile stresses on the magnet. However, their size remains far below the allowable Border. The magnetic flux generated by the rotor enters stators on both sides and uses the currents of the stator winding to create the peripheral forces. The ring-shaped magnet sequence corresponds to two ring-shaped stators. The winding can be designed as a multi-phase winding and essentially lie in a plane perpendicular to the machine axis. It consists of individual coils, which are preferably made of copper round wire or stranded wire, the thrust-forming Currents flow in the radial conductor parts. Require small winding losses limited pole pitches, so that the coil part, which does not act in a thrust-forming manner, extends in the circumferential direction does not become too large compared to the radial part. A small pole pitch is also favorable for limiting the yoke height for the return path of the magnetic River. The yoke is expediently formed from a sheet metal coil, the Sheet thickness is chosen to be lower for high frequencies than for small ones. To a to ensure sufficient magnetic conductivity in the winding space There the synthetic resin used to connect the individual conductors is mixed with iron powder. This enables a conductivity and at the same time a very extensive prevention of eddy currents can be achieved. The embedding of laminated sheet metal stacks in the encapsulated winding also leads to a similar result.

Due to the structure of the stator, a high material utilization is achieved achieved because high magnetic flux densities and large winding layer thicknesses and so that a large current flow per unit length of the circumference can be realized can. The winding layer can be formed by a casting process after it has been previously formed the winding and the introduction of the magnetically conductive teeth. This achieves a high level of operational reliability for the winding. Of the usually The punching process required to produce the grooves is no longer necessary. Use of materials and manufacturing costs can thereby be reduced in comparison with the conventional technology severely limit. In particular, the high circumferential speed that can be achieved contributes to this in that only a small active volume is required. Unlike the synchronous machine with current-carrying conductors in the rotor (salient pole machines) appears in the present case Construction enables a significant increase in peripheral speed.

The shape of the machine described here can achieve be that the active material is mainly arranged only in the field area, where the previously feared punching problems for such machines and the relative large waste of high-quality dynamo sheet can be avoided. The advantages of the ring geometry come to the full in so far as a motor with high peripheral speed is present, but due to the large diameter, no extremely high speeds occur. The disadvantages associated with this, such as larger gear ratios, can largely be avoided will.

3e2 The energy supply and processing The multi-phase three-phase winding is multi-pole and can be divided into several parallel sections, e.g. a, b, c and d according to Fig. 2 can be divided. The winding is supplied with power via several identical ones Inverters (WR a - which are fed via a direct current bus line.

In the simplest case, the inverter can consist of two DC converters exist, the currents shifted by 900 in the two strands of the three-phase winding produce.

The basic frequency of the controller corresponds to the pole change frequency and thus the speed. The size of the current amplitude, which determines the torque, can either through the so-called mlswrfahren, i.e. about influencing the voltage-time area by means of intermediate clocks or by controlling the current via the rectifier or the feeding generator. power supply and processing can be standardized to the extent that the inverter modules for machines of different power and speed on the same voltage and same Electricity can be designed. This may be necessary for the three-phase windings different numbers of turns. Different machine performances require one different number of inverter modules; it is roughly proportional to the strength of the current. The method of modular arrangement of the inverters is not exclusive limited to vehicle drives. A corresponding modular design of the rectifier does not appear to be required with the same urgency because this is due to its simpler nature Structure has less of an impact on total costs.

Figure 3 shows the example of two current controllers in a two-quadrant circuit existing inverter module with a two-strand winding design. the Current controllers d and q each consist of 2 branches, an anti-parallel connection of Transistor Tr and diode D. Several transistors can be used to increase the current intensity connect in parallel. Your ignition power supply can be in the form of the Darlington pair or by connection via an ignition current transformer. The switching properties of the transistors allow the use of a comparatively simple and fail-safe Control logic. The current carrying time of the stator winding is determined with the help of the pole angle control permanently assigned to the local position of the flux distribution generated by the magnets. Through an in-phase allocation of current and field distribution without interconnection of control loops is a dynamic high quality and with regard to the thrust yield very cheap solution achieved. As with a DC machine, the voucher is compulsory Allocation of magnetic field and current distribution for the greatest value of the thrust at the smallest Losses of Winding and a low tendency to vibrate Clearing operations. To achieve this goal, the Control logic with information about the position of the magnets in relation to the winding provided. The opening and closing of the switch can thus be in phase and with the frequency corresponding to the pole changes.

In this respect, the size cannot be adjusted via the direct current circuit of the current is given, by specifying certain additional switching cycles the resulting coil current between a maximum value within a basic period and be set to zero. The use of transistors as switching elements leaves Compared to the thyristor, far higher clock frequencies up to 10-20 kHz to. Since several clock cycles are required for each basic period, they are operated in pulsed mode an upper frequency limit of 1 - 2 kHz is given. It thus exceeds the frequency limit the thyristor converter several times over.

When the current is set from the rectifier, 10 - 20 kHz stand for the Base frequency available.

A complete utilization of this frequency range seems to be at the moment not yet to be visible to vehicle technology. The one via a DC bus line connected inverter modules work with an operating voltage that is essential is determined by the reverse voltage of the power transistors. The latter achieved today an upper limit of 1700 - 2000 V. A series connection of transistors does not appear to be absolutely necessary. The waiver of higher operating voltages comes benefit from a simpler insulation technology and the manufacture of the winding. He also corresponds to the desired parallel connection of several inverter modules for power multiplication.

The parallel operation of modules, each with its own control logic leads to multiple redundant energy processing. Also for those on the power units related prices of the rectifier affects the comparatively low operating voltage cheap.

Figure 3 is based on the assumption that there are 2 coils per strand are connected in series. This corresponds to a winding sector with 4 poles.

Except for the two-quadrant circuit of the controller, which is a split the DC voltage source with two opposing partial potentials is required without a center tap, a four-quadrant connection of the controllers to choose from. she owns the advantage of only one direct current bus line, but leads to the utilization of components to similar results as the circuit according to Figure 3.

3.3 Further variants of the drive motor Different conditions of use can define the criteria for the desired operating characteristics and the design parameters shift in different directions. So the desire for particularly inexpensive Motors with regard to the state of magnet technology the tendency to motors convey with just one rotor.

In connection with the possibility of saving losses (Iron losses) the dualex arrangement of Fig. 4 in Fig. 3 appears interesting. It represents a corresponding motor design with only one stator and two rotors Here, too, is to improve the magnetic conductivity in the middle range the winding is filled with iron powder or iron blocks laminated in the direction of flow been assumed. The field inference i ¢ p circumferential direction can be within the Rotors are made in solid soft iron.

Since the magnetic field does not change over time there, none occur Iron losses. The latter are limited to the area of the teeth of the winding. The plastic-encapsulated winding has the circumferential forces and due to inhomogeneities of the magnetic field occurring residual forces in the axial direction.

The division of the winding, which is desired for circuit reasons into two independent halves is through a separation along the axial middle half possible (see section 4).

A performance increase with a fixed diameter of the motor is through an addition to the number of rotor and stator rings is possible. These for disc motors known measures may give rise to further adaptation or modification of the be the design previously described. For example, a stator arrangement used on both sides also be designed with a common winding. This can be used as a ring winding enclose a yoke fed on both sides.

Figure 4 A shows how a partial support of the Flich forces the magnet on the yoke ring and the outer support ring is achieved. The magnets are divided into inner (i) and outer (a) cuboid blocks, with the inner Cuboid is supported by a reinforcement of the yoke ring. The magnets become functional glued.

With the help of the outer support ring, the centrifugal forces of the outer Magnet row are caught without the yoke ring is overstressed. Height Circumferential speeds with sufficient mechanical security can thus be achieved.

4. Measures to influence the torque and to limit the voltage 4. 1 Field weakening When operating without manual gearbox, vehicle motors have small ones Speeds produce large torques while in the upper speed range significantly lower forces are required. The limit curve of the relationship between Torque and speed correspond approximately to a curve of constant power. In order to create favorable conditions for the dimensioning of the frequency converter, the magnetic flux is usually weakened with increasing speed. Through this it can be achieved that in the relevant operating range the product of flux and frequency (the latter is proportional to the speed); and thus the operating voltage, remains roughly constant The current from converter and then also remains constant Machine.

For motors with permanent magnets, the method of field weakening can be used also realize. The change in the magnetic Serve conductivity of the flow path. The latter can in turn by shifting of machine parts in the axial or in the circumferential direction.

Machines according to Figure 4 can be equipped with axially displaceable rotors, for example carry out. This corresponds to an increase in the gap between the magnet and the stator the desired reduction in magnetic conductivity and thus a reduction in size of magnetic flux.

The rotation of one of the two rotors up to a maximum of one pole pitch in the circumferential direction causes a reduction in the winding flux to almost the Value zero, because then two magnets of the same polarity are facing each other.

A shift appears to be better executable than a rotor shift one half of the winding in the circumferential direction.

Because with the help of an iron enrichment in the tooth zones areas are good magnetic conductivity with such poor conductivity in the coil area alternate, a shift by one tooth pitch can cause that in the In the middle between the two windings, there is a change in conductivity. This is synonymous with a greatly reduced conductivity, which corresponds to a minimum value of the flow. It appears to be an advantage that even a small path in the circumferential direction of a corresponds to a large field change. An electric actuator can be used as the actuator to serve. The movement of the winding half can therefore be relatively low-friction occur because the residual magnetic forces occurring in the axial direction are low are.

4. 2 phase swiveling process by shifting the winding without direct Influencing the magnitude of the magnetic flux can limit the voltage interspersed with the same magnetic field by phase swiveling between two similar types Winding halves are brought about when these are electrically connected in series are.

A shift of one half to one pole pitch means a voltage drop to zero and an equal reduction in torque. The method can be implemented both with machines according to Figure 1 and those according to Figure 4 4.3 Voltage and torque influencing by winding changeover By disconnecting of a winding part, the effective number of turns can be changed, so (ß for the The same effect is achieved as with a voltage induced in the winding Field weakening. Figure 5 shows the switch built in the middle of the winding Sd and Sq in position II; one that has been cut by half is equivalent to.

In the starting range, at low speed, the switch position is I is used, which brings all poles of the magnetic field into effect in a thrust-forming manner.

In Figure 6a, in addition to the torque curve, M / Mmax is plotted against the angular velocity # the induced voltage is also plotted. It increases in with the full number of turns Switching position I is linear and becomes constant through field weakening from Q / n max = 0.125 held. The flux function corresponds to the curve of the moment function as in Figure 6b shows; The power level remains unchanged. Used at max = 0.25 with switch position II halves the number of turns, the Flux can be raised to the maximum value again. The induced voltage increases as a result returns to the previous value (shown in dashed lines). To this value not to exceed, the flow must be weakened at higher angular velocities, like picture 6b shows. The current load remains constant and limited in the entire area however, to half the size of the mass.

Between the speed limits Compared to a machine with a constant number of turns, only half of the winding losses occur.

With one divided into 3 sections connected one behind the other Winding can switch the switching process at two thirds and one third of the maximum torque as shown in Figure 7a. The corresponding flow course is shown in Figure 7b, which belongs to the limit curve of the torque. Here, too, is the local power level constant regardless of the angular velocity. The winding losses suffered in switching positions II and III two thirds and one third of the losses of the Approach area. The winding changeover procedure evidently offers a possibility represents to greatly reduce the winding losses at higher speeds. There In the present case, designs with a low-iron stator are described the winding losses in the foreground. Their reduction therefore leads to a strong one Increase in overall efficiency. The execution of machines with on and off switchable Poles of the rotating field winding correspond to the task set for vehicle drives to generate particularly high torques in the start-up area.

For the choice of switch it is noteworthy that the switching process can be done without current, since the inverter itself is an actuator with a switching function and can be temporarily blocked for this purpose. Regarding the electrical The switching properties are therefore not subject to high demands on the switches. Under these facilitating conditions, conventional switches can be very reliable can be used and at the same time achieve very high numbers of switching cycles.

The method of changing the number of turns in steps becomes useful in connection with the field influence applied in such a way that voltage peaks and thrust collapses are largely avoided.

Claims (3)

5. Protection claims 1. Synchronous machine consisting of at least one Rotor, the magnetic field by permanent magnets without a live winding generated and at least one stator that carries the multi-phase three-phase winding, d a u c h e k e n n nz e i c h n e t that the magnetic flux breaks the air gap penetrated in the axial direction and the centrifugal force arranged in an alternating sequence Permanent magnets from a non-magnetic ring arranged outside the magnets be recorded, the magnetic flux in the circumferential direction either in a belonging to the stator from dynamo sheet metal or belonging to the rotor Discs made of solid soft iron are used to transmit power to the Find hub with use; in addition, that the multi-pole multi-phase winding with radially arranged conductors in the magnetic field contains pronounced coils, whose intermediate areas are potted with plastic, in the zone of the magnetic field Conductivity-improving ferromagnetic fillings are used, the The winding surface is smooth on the outside and the winding layer as a whole is able to absorb circumferential and normal forces and to structural elements of the stator with which it is connected. 2. Synchronous motor according to claim 1 d a d u r c h g e k e n n z e i c h n e t that the multi-pole multi-phase winding in sections via 2- or 4-quadrant controllers of the same design (DC chopper) from a common DC bus is fed with alternating current adjustable in size, the frequency of which is the speed and its phase position of the field distribution of the Is assigned to the rotor, whereby the flow distribution is determined via a measuring element. 3. Synchronous machine according to claims 1 and 2 d a d u r c h g e It is not possible to say that the magnetic force is responsible for the influence of tension and tension Flux by changing the magnetic conductance such as by axial displacement the rotors or by rotating the stator halves in the circumferential direction, or that without a change in flux, the voltage can be influenced by twisting the winding halves, which are electrically connected in series is achieved. 4 * synchronous machine according to claims 1, 2 and 3 d a d u r c h g e k e n n n e i n e t that a DreLmo.l, de- and tension-influencing step by step takes place in that the stator winding is divided into several sections, the can be connected in series by switching elements or partially switched off, the switched-off winding units remain open and the switching process without current and in connection with measures to influence the flow.