Induction machines

Abstract

The invention relates to a novel type of electric inductance arrangement for a series of applications in the field of distance measurement, sensor-based detection of objects, and construction of induction machines. The novelty consists in the type of inductance arrangement of the receiver or transmitter coil, said arrangement being designed in the form of a ladder rung arrangement, wherein the ladder spars short-circuit the rungs. The sum of all the short-circuit currents is an indicator of what is occurring in the surroundings of the arrangement. This could be changing magnetic fields caused by transmitter objects or additional ladder-rung systems acting as transmitters. Multiple such sensors and transmitters can be designed in the ladder-rung form, said sensors and transmitters being connected in parallel or in series according to the application under certain circumstances and if necessary assuming the excitation function by moving a conductor through which a direct current is flowing or by applying alternating currents. The aforementioned inductance arrangement results positively in that the coils can all have a completely crossover-free design and are therefore substantially simpler to technically implement for very different applications in electrical engineering. The applicability ranges from short-range distance measuring devices and long-range object location to light detection and efficient induction machines with large or also very small constructions.

Claims

1. Inductance system as application in induction machines having two or more primary inductance arrangements as the stator (10) and at least one secondary inductance arrangement (11, 12) as a rotating or linearly driving unit, wherein the primary inductance arrangement (10) and the secondary inductance arrangement (11, 12) are configured as ladder-rungs arrangement comprising electrically conductive rungs (14, 14a-14c) and connecting them spars (15, 15a-15c), characterized in that the impedance of the spars (15, 15a-15c) in relation to the impedance of the rungs (14, 14a-14c) is of lower impedance and the impedance of a short-circuit measuring and/or driving arrangement built into the inductances system at the measuring terminals (i1, i21, i22) again is of even lower impedance and the sum of the induced rungs currents (i.sub.L/n) in each rung (14, 14a-14c) is measurable at the measuring terminals (i1, i21, i22) and that the primary inductance arrangement (10) and the secondary inductance arrangement (11, 12) are arranged without crossing.

2. Inductance system according to claim 1, characterized in that the current flow of all induced rung currents (i.sub.L/n) in each rung (14, 14a-14c) is directed at any time in the direction of the short-circuit measuring device or is directed away from it.

3. Inductance system according to claim 1, characterized in that the primary inductance arrangement (10) and/or the secondary inductance arrangement (11, 12) are configured as flat or as a flat rolled-up or as a planar ladder-rung arrangements.

4. Inductance system according to claim 1, characterized in that at least one of the rungs (14, 14a-14c) has only one winding turn.

5. Inductance system according to claim 1, characterized in that the inductance system comprises a housing (9) made of high-permeability magnetic material.

6. Inductance system according to claim 1, characterized in that the cross sections of the rungs (14, 14a-14c) are different from each other.

7. Inductance system according to claim 1, characterized in that the primary inductance arrangement (10) and the secondary inductance arrangement (11, 12) consists of conductive material with different kind of level of electric resistance depending on the material to be used for the rungs (14, 14a-14c) and/or cross section of the rungs (14, 14a-14c).

8. Inductance system according to claim 1, characterized in that the primary inductance arrangement (10) and/or the secondary inductance arrangement (11, 12) consists of different kinds of conductive metallic materials.

9. Inductance system according to claim 1, characterized in that the geometry for the inductance system in static, stationary or unsteady moving ladder-rungs arrangements by way of using computer-aided three-dimensional simulation tools can be determined virtually by calculation and optimization and validated as suitable for the particular application.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 describes the system of Maxwell's equation.

(2) FIG. 2 described quasi-stationary electromagnetic fields.

(3) FIG. 3 shows an LVDT (Linear Variable Differential Transformer) as an analog sensor for displacement measurement.

(4) FIG. 4 shows a half-symmetry display of an LVDT field domain including the complete external circuitry after the automatic discretization has been performed.

(5) FIG. 5 shows a finite element-illustration of an exemplary LVDT in half-symmetry.

(6) FIG. 6 shows the amplitude of the complex sensor output voltage U as a function of the path coordinates.

(7) FIG. 7 shows the representation of the magnetic field lines for the example LVDT.

(8) FIG. 8 shows the magnitude of the magnetic field strength HSUM [A/m] from simulation of the example LVDT.

(9) FIG. 9 shows the magnitude of the electromagnetic flux density BSUM [T] from simulation for the example LVDT.

(10) FIG. 10 shows the vector of the magnetic field strength H [A/m] from simulation for the example LVDT.

(11) FIG. 11 shows the vector of the electromagnetic flux density BSUM [T] from simulation for the example LVDT.

(12) FIG. 12 shows a simple, new LVDT arrangement, which was described for the first time within the scope of the BMWi funding program PRO INNO II under FKZ KU0568901RR7.

(13) FIG. 13 shows the sensor characteristic U(s) of the inductive displacement sensor from FIG. 12 with a signal generator/construction length ratio of 0.5:1.

(14) FIG. 14 shows the sensor characteristic U(s) of the inductive displacement sensor of FIG. 10 at a signal generator/length ratio of 0.1:1.

(15) FIG. 15 shows the finite elements representation of an LVDT with interlaced secondary coils in half-symmetry, e.g. to avoid zero-point errors.

(16) FIG. 16 shows the equation systems used for the transfer of voltage-guided coils into equivalent current-carrying coils.

(17) FIG. 17 shows the arrangement of inductive displacement sensors with planar coils and shows by way of example a planar inductive displacement sensor in layer construction with a total of four layers.

(18) FIG. 18 shows to a flat displacement sensor in ladder-rungs arrangement, layer 0: shielding (9), layer 1: the primary grid (10) as a feed-in system.

(19) FIG. 19 describes a flat displacement sensor in ladder-rungs arrangement with layer 2: first secondary grid (11).

(20) FIG. 20 describes a flat displacement sensor in ladder-rungs arrangement, layer 3: second secondary grid (12).

(21) FIG. 21 describes a flat displacement sensor in ladder-rungs arrangement having layer 4: transmitter (13) shown over layer 3: second secondary grid.

(22) FIG. 22 shows the calculated path characteristic of a planar inductive displacement sensor in 2D printing technique in ladder-rungs arrangement according to FIG. 18 to FIG. 21.

(23) FIG. 23 illustrates how the flat displacement sensor in ladder-rungs arrangement in accordance with FIG. 18 to FIG. 21 is converted into a planar angle sensor by polar coordinate transformation.

(24) FIG. 24 shows by way of example an angle characteristic calculated analogously thereto.

(25) FIG. 25 shows a cylindrical inductive displacement sensor in 2D/3D-rolling technique with three turns per winding loop.

(26) FIG. 26 shows the improved linearity of a cylindrical inductive displacement sensor in 2D/3D-rolling technique with three turns per winding loop.

(27) FIG. 27 shows a cylindrical inductive displacement sensor in 2D/3D-rolling technique with three turns per winding loop.

(28) FIG. 28 shows fully interlaced secondary coils at significantly improved linearity.

(29) FIG. 29 shows a schematic representation of a trapezoidal bar code label with associated rungs (14) and spars (15).

(30) FIG. 30 shows the associated planar sheet metal section for an inner rotor with 28 slots.

(31) FIG. 31 shows the strand axes perpendicular to each other.

(32) FIG. 32 shows the design of the windings in the main and auxiliary line done by means of sinusoidal turns.

(33) FIG. 33 shows a quarter section of the two-strand induction motor along the axis of rotation.

(34) FIG. 34 shows that the one strand, the so-called main strand is connected directly to the power network, the second strand, the so-called auxiliary strand, via a capacitor.

(35) FIG. 35 shows a total of three ladder-rungs assemblies which are to replace the traditional windings of this two-strand asynchronous motor.

(36) FIG. 36 illustrates the operation of a band wound asynchronous motor, the numerically determined transient current waveform of the two phases A and B.

(37) FIG. 37 shows, as an example, a two-strand induction motor.

DETAILED DESCRIPTION

(38) FIG. 12 shows a simple, new LVDT arrangement, which was described for the first time within the scope of the BMWi funding program PRO INNO II under FKZ KU0568901RR7. Here, the path information is encoded by means of progressively increasing number of turns of the secondary coils. The secondary coils are symmetrical to the sensor center. The finite element representation of this LVDT with overlapping secondary coils in half-symmetry shows the cross-sectional area rendered with the material assignment: stainless steel pressure tube (2), primary coil (inside) (3) secondary coil 1 (left) (4), the secondary coil 2 (right) (5), left and right front disc (6), housing (7), air environment (8).

(39) An essential feature of the encoded path information is that the shape and size of the signal generator is not critical for the path characteristic U(s). The size of the signal generator only has an influence on the maximum size, i.e. the amplitude of the path signal.

(40) FIG. 13 shows the sensor characteristic U(s) of the inductive displacement sensor from FIG. 12 with a signal generator/construction length ratio of 0.5:1. The characteristic curve exhibits a zero-point offset due to its simple construction (output voltage zero does not coincide with the sensor center). This offset error can be eliminated e.g. by interlacing of the secondary coils and/or further measures, see arrangement in FIG. 15.

(41) In FIG. 14, the sensor characteristic U(s) of the inductive displacement sensor of FIG. 10 at a signal generator/length ratio of 0.1:1 is shown. The signal generator was consciously removed from the coil area on the left and right (bends in the path characteristic) in order to show that the path information is based exclusively on the way the secondary coils are designed. It can be seen that the basic course of the sensor characteristic is maintained, and the size of the signal transmitter only affects the amplitude of the output signal.

(42) FIG. 15 shows the finite elements representation of an LVDT with interlaced secondary coils in half-symmetry, e.g. to avoid zero-point errors. Cross-sectional representation according to FKZ KU0568901RR7 with coding of the material allocation: Stainless steel pressure tube (2), primary coil (inside) (3), secondary coil 1 (left) (4), secondary coil 2 (right) (5), left and right end disc (6), housing (7), air environment (8).

(43) The invention describes a fundamental simplification for all inductive conductor arrangements by standardizing the geometry of such conductors by one or more short-circuited ladder-rungs arrangements which influence each other, under certain circumstances, each with several short-circuited turns in space, wherein the sum of the short-circuit currents becomes a clear indicator of the spatial distance and positioning of a magnetizable object, for example. With the aid of lithography techniques and thin films, such ladder-rungs arrangements are very easy to produce by means of printing processes and can either be arranged in space, or assume any rolled-up or spiral shape in space that a wound or spirally wound film allows. One, several or any number of such ladder-rungs foils can be arranged arbitrarily in space and optionally serve as sensor(s) or transmitters. The distances between the short-circuited rungs in space can be equidistant or the distances vary, for example with a constant factor X increasing. The distance, the length and the cross section of the short-circuit strands in relation to each other are also variable, the ladder spars can be arbitrary in space and be designed trapezoidal, for example, or follow any curves in the plane or in space, and the short-circuit strands can be designed with changing cross section. These variations can also occur in a mixed fashion, for example in the form of an arbitrary three-dimensional barcode.

(44) By way of example, the ladder-rungs arrangement describes as a new claim the arrangement of crossing-free planar and spatial coils by canonical transformation.

(45) The aim of the new approach is to design the electromagnetic flux density in space in such a way that its distribution does not depend on the shape and size of the signal transmitter, nor on the housing or its boundaries. For this purpose, according to the Nyquist sampling theorem, conductor patterns are arranged as reference points in the space in such a way that arbitrary path coordinates can be detected including local refinement by means of barcodes or vernier coils. This approach can be both inductive and capacitive and is directly suitable for all axial two-quadrant displacement sensors, all four-quadrant path sensors, planar and cylindrical angle encoders, proximity sensors and proximity switches, linear combinations of the aforementioned subsystems and new applications of far-field electromagnetic field measurement at moderate signal frequencies.

(46) An essential prerequisite for dimensionally stable execution of electromagnetic coils in a space are high- and highest-resolution batch processes for the production of conductor patterns. Preference is given to these production methods, which have been established for more than four decades in the field of “Printed Circuits” (see Methods of Thin Film or Thick Film Technology, amongst other things, from the Globaltronics 2010, Sep. 13-15, 2010, Singapore). These include classic multi-layer flexible circuits, paste-based offset printing on carrier films with optional release of carrier film during assembly, industrial inkjet techniques, dispensor tapes with pre-assembled conductor patterns for placement machines, and many others. Another goal is to simplify the construction of windings for electromagnetic machines with extreme drive power. For this, windings in punching or rolling technology or by injection molding are considered.

(47) The printed circuit manufacturing processes provide multi-layer flexible conductor patterns with a limited number of vias between individual layers. However, plated-through holes are comparatively expensive and very space-consuming for larger current densities. As a result of this situation, conventional sequential windings in printing technology are not realistic for large power requirements.

(48) In electrical engineering, current and voltage sources are considered dual as the basic equivalent circuits for feeding passive and active circuits. The task is to convert voltage-guided coils into equivalent current-carrying coils in the course of a canonical transformation. The general expectation is that, when transitioning from the voltage range to the current range, the primary voltages decrease with the number of winding turns, and the branch currents increase with the number of winding turns while the electric power remains the same. Furthermore, it is expected that a simpler wiring specification can be derived in the current range due to the parallel connection of branch currents, which possibly leads to simpler topologies in print technology in the sense of “printed circuits”.

(49) FIG. 16 shows the equation systems used for the transfer of voltage-guided coils into equivalent current-carrying coils. As can be seen from the comparison of voltage range and current range, a voltage-driven coil according to equation 12 can be converted into a current-controlled coil according to equation 13. The two equations 12 and 13 respectively apply to the application of a generator or sensor, in which the internal electromagnetic flux leads to the supply of an externally connected electrical circuit. As expected, the number of turns occurs as a common scaling factor between the two domains. And in fact the Helix structure of the voltage-driven coil now becomes a completely flat structure, which can be trivially derived from any planar or rotational printing process. Depending on the resistance level of the wire turns Rw in equation 13 operation is with low impedance bus bars. The evaluation of the sensor signal is typically carried out at the signal terminal voltage zero, i.e. virtual short circuit. This virtual short circuit can be done with low impedance wiring. A proven method is the connection of the two current-controlled coil terminals to the input of an operational amplifier, which is connected as a current/voltage converter.

(50) Similarly, a voltage-driven coil according to equation 14a, b can be transformed into a current-controlled coil according to equation 15a, b. Equations 14 and 15 respectively apply to the case of application of a motor or a field source in the case of the sensor arrangement in which the internal electromagnetic flux is generated by an electrical circuit connected externally. Here, too, the number of turns occurs as a common scaling factor between the two domains, and the helical structure of the voltage-driven coil can be converted once more into a completely planar structure.

(51) The canonical transformation of voltage-guided coils into those with current guidance and vice versa is a basic mapping from the circuit theory, and can therefore be used for any application. With respect to the task of displacement measurement a flat printed circuit is first discussed, which may be constructed without restriction as a film circuit.

(52) As one of the many possible embodiments of the invention, FIG. 17 shows the arrangement of inductive displacement sensors with planar coils and shows by way of example a planar inductive displacement sensor in layer construction with a total of four layers. The primary coil (10) in layer 1 consists of a ladder-rungs arrangement consisting of rungs (14a), spars (15a) and an alternating current i1 impressed on the spars. The primary coil operates as a field generator according to equation 15a, b with bottom field foil (9) based on mu-metal in layer 0. The first secondary coil (11) in layer 2 with ladder-rungs arrangement consisting of rungs (14b), spars (15b) and an alternating current i21 impressed on the spars and the second secondary coil (12) in layer 3 with ladder-rungs arrangement consisting of rungs (14c), spars (15c) and an alternating current i22 impressed on the spars work as displacement sensors, which are encoded with a path information in the form of a progressively increasing or decreasing conductor density. All four layers are stacked vertically and are insulated from each other. In the uppermost layer 4 runs a freely movable, soft magnetic position transmitter (13). The terminals of the two secondary coils are each connected to a separate current/voltage converter. From their outputs, the path signal is finally determined by subtraction. In the simplest case, it is sufficient to switch the two secondary coils in parallel. The current difference can then be formed with a purely passive circuit (ohmic resistance).

(53) The configuration of the displacement sensor in FIG. 17 can be extended as follows:

(54) a) Four-quadrant displacement sensor:

(55) Layer 0: mu-metal Layer 1: primary coil rotated by 45° Layer 2: secondary coil 1 Layer 3: secondary coil 2 Layer 4: copy of secondary coil 1 rotated by 90° (secondary coil 3) Layer 5: copy of secondary coil 2 rotated by 90° (secondary coil 4) Layer 6: position transmitter, which can be detected in the entire plane (four quadrants).
b) Four-quadrant displacement sensor as a flat angle encoder: Layer 0: mu-metal Layer 1: primary coil rotated by 45° Layer 2: secondary coil 1 Layer 3: secondary coil 2 Layer 4: copy of secondary coil 1 rotated by 90° (secondary coil 3) Layer 5: copy of secondary coil 2 rotated by 90° (secondary coil 4) Layer 6: position transmitter, which rotates over the entire plane.
c) Two-quadrant displacement sensor as a flat angle encoder: Layer 0: mu-metal designed as a flat circular band Layer 1: primary coil designed as a flat circular band Layer 2: secondary coil 1 designed as a flat circular band Layer 3: secondary coil 2 designed as a flat circular band Layer 4: position transmitter which rotates along the circular band structure.
d) Two-quadrant displacement sensor as a cylindrical angle encoder. Layer 0: mu-metal Layer 1: primary coil Layer 2: secondary coil 1 Layer 3: secondary coil 2 Layer 4: position transmitter, which rotates along the cylinder jacket. The entire assembly is rolled up around the vertical axis in a cylinder with 360°.
e) Four-quadrant displacement sensor as parabolic far field sensor: Layer 0: mu-metal Layer 1: primary coil rotated by 45° Layer 2: secondary coil 1 Layer 3: secondary coil 2 Layer 4: copy of secondary coil 1 rotated by 90° (secondary coil 3) Layer 5: copy of secondary coil 2 rotated by 90° (secondary coil 4) Layer 6: metallic position transmitter, at some distance e.g. >1 m. The entire assembly is cured, for example, in a parabolic bowl with adhesives. To obtain an electromagnetic directional characteristic. This can be used at low frequencies already.

(56) In FIG. 18-21 it is shown that planar sensors can be built in virtual reality quite the same way as the ladder-rungs arrangement described in FIG. 17.

(57) FIG. 18 shows to a flat displacement sensor in ladder-rungs arrangement, layer 0: shielding (9), layer 1: the primary grid (10) as a feed-in system.

(58) FIG. 19 describes a flat displacement sensor in ladder-rungs arrangement with layer 2: first secondary grid (11).

(59) FIG. 20 describes a flat displacement sensor in ladder-rungs arrangement, layer 3: second secondary grid (12).

(60) FIG. 21 describes a flat displacement sensor in ladder-rungs arrangement having layer 4: transmitter (13) shown over layer 3: second secondary grid. The extension of the transmitter transversely to the movement in the direction of the y-axis is not decisive for the task of measuring distance, as long as its cross section Aa, i.e. its projected area on the layers 1 to 3, remains constant during the movement.

(61) All arrangement shown in FIG. 17 to FIG. 21, FIG. 23, FIG. 25 and FIG. 27 as well as FIG. 30 to 37 were calculated with the help of computer-aided simulation workflows, and verified according to the desired or planned action and functionality, and thus validated virtually in terms of their functionality.

(62) The same applies to any geometric alternate embodiment of the multilayer printed circuit ladder-rungs configurations.

(63) FIG. 22 shows the calculated path characteristic of a planar inductive displacement sensor in 2D printing technique in ladder-rungs arrangement according to FIG. 18 to FIG. 21: sensor characteristic I(s). Dual, planar crossing-free form to LVDT displacement sensor in FIG. 12 with wire grids with significantly better linearity. I1 is the signal current in the secondary grid 1, I2 is the signal current in the secondary grid 2, (I1+I2) is the total current of the two secondary grids with the expected linear path characteristic. Unlike in FIG. 15 no corrective measures have been applied to the two secondary grids yet. Compared to the LVDT in FIG. 15, this current-driven displacement sensor operates at a fraction of the electrical operating power. The calculated number of ampere-turns of the primary grid is only Aw=1 A.

(64) FIG. 23 illustrates how the flat displacement sensor in ladder-rungs arrangement in accordance with FIG. 18 to FIG. 21 is converted into a planar angle sensor by polar coordinate transformation, which covers all four quadrants and can continue to be used as a resolver for continuous rotational movements. FIG. 23 shows the view of the two secondary grids and the angle transmitter, which rotates around the center of the polar coordinate system. The primary grid and the shielding foil according to FIG. 18 are behind it. Rotationally symmetric structures allow an ideal formulation of the boundary conditions for electromagnetic fields. For example, here the electrodes for feeding the currents into the primary and secondary grids can be kept very slim. This makes it possible, for example, to design small structures for an extended frequency range. FIG. 24 shows by way of example an angle characteristic calculated analogously thereto.

(65) Ladder-rungs structures can be extended almost arbitrarily and thus become very large depending on the size of the covered area. For practical reasons, it is advisable in such cases to arrange transmitter and receiver systems, either periodically sequenced, hierarchically and/or in a matrix form. The necessary identification or differentiation of multiple ladder-rungs based transmitters and receivers can be done, for example, with barcode labels, which have different codes on the variance of distance and cross section of the rungs, possibly in conjunction with e.g. trapezoidal or otherwise curved arranged spars. FIG. 29 shows a schematic representation of a trapezoidal bar code label with associated rungs (14) and spars (15).

(66) Another possible embodiment is described below in the form of inductive displacement sensors with non-crossing cylindrical coil.

(67) From equation 13 it can be seen that current-controlled coils are also possible in the form of a series/parallel circuit. To do this, in equation 13, each individual turn is passed through several times before the shorting bars are contacted. The purpose of this arrangement for sensors is to achieve a higher electromagnetic flux. In addition, by these measures, the individual turns accumulate higher impedance, so as a rule an operational amplifier for evaluating the sensor signal can be dispensed with. This also makes it possible to use power circuits with no intersection technology. That is, this method is applicable to field sources and all induction generators, and more generally suitable for the construction of electromagnetic machines at low impedances.

(68) FIG. 25 shows a cylindrical inductive displacement sensor in 2D/3D-rolling technique with three turns per winding loop, each for the upper secondary coil (11) or for the lower secondary coil (12), signal transmitter (13), not shown primary coil. The axial section shows a dual crossing-free form to LVDT displacement sensor from FIG. 5 with half coils exhibiting a significantly improved linearity.

(69) The improved linearity of a cylindrical inductive displacement sensor in 2D/3D-rolling technique with three turns per winding loop is shown in FIG. 26. The sensor characteristic I(s) occurs in the following manner: I1 is the signal current in the secondary coil 1, I2 is the complementary signal current in the secondary coil 2, (I1+I2) is the total current of the two secondary coils with the expected linear path characteristic. Unlike FIG. 5, no corrective measures were applied to the two secondary coils. Compared to the LVDT in FIG. 5, this current-carrying displacement sensor operates at a fraction of the electrical operating power. The calculated number of ampere-turns of the primary winding being Aw=1 A only.

(70) FIG. 27 shows a cylindrical inductive displacement sensor in 2D/3D-rolling technique with three turns per winding loop, each for the upper secondary coil (11) or for the lower secondary coil (12), signal transmitter (13), primary coil not shown. The axial cut shows a dual intersection-free shape comparable to LVDT displacement sensor from FIG. 15 with fully interlaced secondary coils at significantly improved linearity, which is shown in FIG. 28. The sensor characteristic I(s) is calculated as follows: I1 is the signal current in the secondary coil 1, I2 is the opposite signal current in the secondary coil 2, (I1+I2) is the summation current of the two secondary coils with the expected linear path characteristic. Unlike FIG. 15, no corrective measures were applied to the two secondary coils. Compared to the LVDT in FIG. 15, this current-driven displacement sensor can handle a fraction of the electrical operating power. The calculated number of ampere-turns of the primary winding is only at Aw=1 A.

(71) A further possible form of application for crossing-free planar and spatial coils will be described below for use in induction machines.

(72) As stated above, current-controlled coils are also possible in the form of a serial/parallel connection. To do this, in equation 13, each individual turn is passed through several times before the shorting bars are contacted. The number of cycles is limited only by the available winding space. The purpose of this arrangement for induction machines is to achieve higher electromagnetic fluxes while keeping impedances low. In addition, by these measures, the individual turns achieve higher impedances, so that power amplifiers for impressing the strand currents can be dispensed with in most cases. Also, the requirements for the bus bar distribution become significantly lower. Thus, in particular power circuits in crossing-free technology are possible, which can be installed very easily and also be serviced later. That is, this method is applicable to field sources of all kinds and all induction generators, and more generally suitable for the construction of high-speed electromagnetic machines and energy converters even with high power.

(73) In the FIGS. 30 through 37, a two-strand induction motor is described as an example. FIG. 30 shows the associated planar sheet metal section for an inner rotor with 28 slots. The stator has 24 slots. In this very common engine, the angular offset is expressed as an electrical angle alpha=90°. The strand axes are therefore perpendicular to each other, as shown in FIG. 31. The one strand, the so-called main strand is connected directly to the power network, the second strand, the so-called auxiliary strand, usually connects via a capacitor according to FIG. 34. The design of the windings in the main and auxiliary line is often done by means of sinusoidal turns, e.g. the turns in FIG. 32, differently designed for the main line (phase A) and the auxiliary line (phase B).

(74) FIG. 33 shows a quarter section of the two-strand induction motor along the axis of rotation. Here, the winding heads of the main windings A (outside) and the auxiliary windings B (inside) are to be seen and also the short circuit ring of the cage winding in the internal rotor.

(75) The FIG. 35 shows a total of three ladder-rungs assemblies which are to replace the traditional windings of this two-strand asynchronous motor. The two ladder-rungs arrangements, which are each duplicated, show the development of exactly one stator circulation for the main line (phase A, top) and the auxiliary line (phase B, center). The phase current of the phase A flows through the spar at the top left, passes through the stator in a positive direction downwards (slots A2-A11) and continues to traverse—after accumulation in the lower spar—the stator in a negative direction upwards (slots A14-A23) and finally leaves this 360° development to the right. In the simplest case, the lower spar ends after 360°, and the two upper spars are crossed out, so that the conductor structure repeats modulo 360°. In this case, one obtains a parallel/series circuit per 360° segment and impedance ratios, which come close to those of a classically wound stator for an asynchronous motor. In a common case, all three spars are drawn analogous to development of the rotor in the lower third of FIG. 35 until all the winding layers are traversed. The impedance of the purely parallel ladder-rungs is lower. The description of the ladder-rungs arrangements for the auxiliary line is analogous.

(76) In general, one can implement the discussed ladder-rungs structures either on a carrier tape, that can be optionally removed at the winding of the motor (pure conveyor belt). In this case, the duplicated structure is realized as the front and back of one and the same tape. In this case, it is also possible to apply ferromagnetic layers (9) so that a stator is formed by simple winding of two such tapes, one each for phase A and phase B. For the rotor, only a single tape is needed. In high performance asynchronous motors, it is advantageous to realize the ladder-rungs as endless stamped parts, which are centrally folded in the longitudinal direction in the case of the stator windings. For the magnetic field guidance then usual stacks of sheet metal made of electrical sheet or molded parts made of ferrite are used for the stator or rotor.

(77) To illustrate the operation of a band wound asynchronous motor, the numerically determined transient current waveform of the two phases A and B in FIG. 36 are used (seven 60-Hz periods) and a snapshot from the transient course of the vectorial electromagnetic induction for the instant of time t=35 ms.