The present invention describes an electric rotary machine, method of operation of the electric rotary machine and use of the electric rotary machine in a electric power generation or a mechanical drive system. The electric rotary machine uses electric currents and magnetic materials for conversion between electric and mechanical energy.

More specifically, this invention is a further development of PCT/CH2022/050028 disclosing a structure and method of operation of a brushless, variable-speed electric rotary machine, whose stator windings can be directly connected to an AC electric power supply of constant angular velocity, like for example 50Hz grid, and the rotor comprising a power converter, can spin at variable speed, still reaching close to 100% efficiency.

The problem this invention attempts to solve is that existence of more than one rotating magnetic field within the electric rotary machine might cause injection of asynchronous currents into the AC electric power supply and torque vibrations.

The solution is to use magnetic fields having different number of polepairs. It is namely possible to choose number of magnetic pole-pairs of the second magnetic field, such that asynchronous currents induced in different stator winding sections compensate each other, when those winding sections are connected in parallel, or anti-parallel manner and no asynchronous current is injected into AC electric power supply. Generation of at least two magnetic fields on the rotor side can be facilitated either by separate types of rotor windings: first type generating the first magnetic field and second type generating the second magnetic field, or by the same set of rotor winding employing the concept of rotor current distribution. Further magnetic fields can be used to cancel remaining harmonic current injection into the AC electric power supply, or torque vibrations resulting from nonlinear properties of magnetic material of stator or rotor core. Adding relays into the rotor structure can improve reliability or extend the operating range of the machine if fractional power converter is used on the rotor side.

The major advantages of the disclosed here electric rotary machines and control methods are:

- the terminals of stator windings can be directly coupled to AC electric power supply and if the AC electric power supply is a high voltage supply, there is no need for expensive electronic switches that have to withstand the high voltage of the supply network. Stator can even be connected to such a high voltage supply, for what electronic switches are even not available and that eliminates the need of a voltage-reducing transformer that is normally inserted between AC electric power supply grid and the rotary machine.

- the electric rotary machine can rotate at broad range of angular speed, can easily change direction, or mode of operation: generator, or motor, still being supplied from the same AC electric power supply, whose magnitude and frequency is constant. Electric machines disclosed here can even rotate at larger angular velocity than the angular velocity of the supply network WS. the rotor of the basic version of the electric rotary machine doesn't need any brushes, exciters or any extra elements to transfer electrical power to the rotor, other than rotor windings. - it is possible to generate more magnetic fields in order to cancel out harmonic currents generated in stator windings, so no harmonic currents are injected into the AC electric power supply.

- additional magnetic fields can be generated to cancel out mechanical vibration of the electric rotary machine.

- adding relays into the rotor structure allows improving reliability of the electric rotary machine, so it can continue working despite a single-point failure, like power switch breakdown, or isolation breakdown.

- adding relays into the rotor structure allows extending range of operation, if fractional power converter is used on the rotor side.

- the rotor power switches on the rotor side are better protected against surges, or voltage spikes that might happen on the AC electric power supply rails due to lighting events, or load switching etc.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred exemplary embodiment of the subject matter of the invention is described below in conjunction with the attached drawings.

Fig. 1 presents a general structure of the disclosed electric rotary machine.

Fig. 2 presents a winding section.

Fig. 3 presents a magnetic field extending in stator and rotor.

Fig. 4 presents voltages induced between terminals of winding sections by a rotating magnetic field.

Fig. 5 presents voltages and currents induced by two rotating magnetic fields in a stator winding composed of two winding sections electrically coupled in a parallel manner. Fig. 6 presents another example of voltages and currents induced in a stator winding composed of four winding sections by two rotating magnetic fields.

Fig. 7 presents an embodiment where winding sections electrically coupled in a parallel manner are arranged to form a three-phase stator windings.

Fig. 8 presents voltages and currents induced by two rotating magnetic fields in stator winding composed of two winding sections electrically coupled in an anti-parallel manner.

Fig. 9 presents an embodiment where winding sections electrically coupled in an anti-parallel manner are arranged to form a three-phase stator windings.

Fig. 10 presents a rotor current distribution.

Fig. 11 presents an embodiment of a rotor winding and rotor power switches for regulating electric current in the rotor winding.

Fig. 12 presents an embodiment of rotor windings to generate two magnetic fields rotating independently and corresponding rotor current distribution.

Fig. 13 presents an arrangement how a magnetic field having two components can be generated by two types of rotor windings in such a way that the first magnetic field doesn't induce voltage in the second type of rotor windings and the second magnetic field doesn't induce voltage in the first type of rotor winding.

Fig. 14 presents an embodiment of the electric rotary machine.

Fig. 15 presents an embodiment of the electric rotary machine comprising compensation of harmonic currents and vibrations.

Fig. 16 presents a stator winding as a serial connection of winding groups. Fig. 17 presents an electric power generation system, wherein the electric rotary machine is driven by a prime mover to generate electricity.

DESCRIPTION

Fig. 1 presents a general structure of the disclosed electric rotary machine.

The electric rotary machine comprises a stator (1) and a rotor (2), wherein the stator (1) is stationary, and the rotor (2) can rotate versus the stator (1) around an axis of rotation. The electric rotary machine can work in motor or generator mode.

The stator (1) comprises a rotor core (12). Since during operation, changing magnetic fields are generated within the stator core, the stator core is made of soft magnetic material, whose coercivity is typically below 100 A/m, to minimize power losses due to material remagnetization. Also, the rotor (2) comprises rotor core (22) that is also made of a soft magnetic material due to the same reasons that apply to stator core (12).

The rotor (2) further comprises plurality of rotor windings (41), (42), (43). Also, the stator (1) further comprises stator windings (51), (52), (53). All rotor windings and all stator windings are made from a material, whose electric conductivity is low enough to minimize power losses due to electric resistance. Most common materials used for stator or rotor windings are copper or aluminum, however the invention is not limited to those specific materials. The windings might be formed from wires, tapes, rods, pipes, or other material shapes. They might contain a single or multiplicity of turns. They might contain winding sections electrically coupled in series or parallel manner. The common function of all those windings is that electric currents flowing through those windings affect magnetic fields extending in rotor (2) and stator (1). Each rotor winding (41), (42), (43) has two terminals of rotor winding (8). Also, each stator winding (51), (52), (53) has two terminals of stator winding (7).

In this disclosure we use a term "electrically coupled" to point that two elements are in electric contact in a broad sense: directly or indirectly by some intermediate components. The electrical coupling can be permanent or possible to disconnect. In this disclosure we use a term "to connect" to describe any activity that results in establishing an electrical coupling between two elements or terminals of the two elements.

The electric rotary machine can be electrically coupled and exchange electric power with an AC electric power supply (13). The AC electric power supply (13) has quantity of f phases and defined angular velocity of AC electric power supply WS. If for example the supply system has a frequency of 50Hz, then the value of WS = 2*pi*50 = 314.15 (rad/sec). In a typical case the quantity of phases f is three or one, but the invention is not limited to those numbers. The AC electric power supply (13) might be for example the power grid, a secondary winding of a transformer, or a local AC grid, where electricity is generated by the electric rotary machine. The electric rotary machine comprises plurality of AC supply connections (27) to provide electrical coupling between its internal elements, like terminals of stator windings (7) and the AC electric power supply (13). Not all terminals of stator windings (7) must be coupled to the AC electric power supply (13). If for example the stator windings (51), (52), (53) had been arranged in a star configuration, instead of delta configuration, one terminal of every stator winding would not be electrically coupled to the AC electric power supply (13).

In this disclosure we use notion of angular velocity instead of frequency, but in every case the frequency is the angular velocity divided by two pi.

The rotor (1) further comprises a rotor DC supply (21). The function of the rotor DC supply (21) is to provide instantaneous electric power needed to drive currents of rotor windings (41)... In most cases, the rotor DC supply (21) is a capacitance, but also other, more sophisticated solution involving voltage regulators, batteries, inductors, switch-mode regulators, etc. might be used. The rotor DC supply (21) is able to absorb variations of electric power supply for rotor windings (41)... only for a short period of time but does not have to deliver or absorb electric power constantly during a steady state operation. The rotor DC supply (21) has two terminals: a positive terminal of rotor DC supply (28) and a negative terminal of rotor DC supply (29).

Rotor power switches (9) provide control of a flow of electric currents between rotor DC supply (21) and terminals of rotor windings (8). During operation, a rotor power switch (9) might be in turn-on state when it can conduct significant amount of electric current, or in turn-off state when it blocks current flow. In an idealized view, in turn-on state the rotor power switch (9) provides an electric short between its two terminals and in turn-off state the rotor power switch (9) provides an open circuit between its two terminals. The rotor power switch has also a control input, typically of electrical or optical nature, and the control input determines if the rotor power switch is in turn-on state or in turn-off state. Rotor power switches (9) might be implemented using known devices, like IGBT transistors, silicon-carbide transistors, silicon power FETs, GaN transistors, or others. Those devices might also be combined with diode elements to form a rotor power switches (9). In order to perform its function, a rotor power switch (9) must be able to conduct maximum electric current of all terminals of rotor windings (8) coupled to the switch (9) when the switch is in turn-on state, withstand maximum voltage induced between terminals of the switch (9) when the switch is in off-state and be able to change between turn-on state and turn-off state sufficiently fast: typically in significantly less time than is the time period of the AC electric power supply (13).

The rotor further comprises a rotor controller (24). The function of the rotor controller (24) is to control state of rotor power switches (9), thus controlling electric currents through rotor windings (41)... To fulfill this function, the rotor controller provides signals into control inputs of rotor power switches (9). If for example rotor power switches (9) are implemented as IGBT or FET transistors, the rotor controller (24) controls electric potentials at gates of respective devices in that way switching respective terminals of rotor windings (8) between positive and negative terminals of rotor DC supply (28), (29). The PWM scheme can be used to control effective voltage applied to a terminal of rotor winding (8). In order to fulfill its function, the rotor controller (24) might contain known devices like FET-, or IGBT-driver, and a microcontroller. The rotor controller (24) might also provide regulatory, monitoring, or fault-detection functions for the electric rotary machine. Furthermore, the rotor controller (24) might perform necessary calculation, regulation, or signal-processing functions. The rotor (2) further comprises a rotor communication unit (25) configured to transmit or receive information. This function is necessary to control the operation of the electric rotary machine: for example, a device or a human supervising the electric rotary machine might send an information about requested torque or speed into the rotor controller (24) by means of the rotor communication unit (25). Similarly, the status information, or fault monitoring information might be sent back from the rotor controller (24) through the rotor communication unit (25).

Fig. 2 presents a winding section.

A stator winding (51) or a rotor winding (41) contains of one or more winding sections (6). Every winding section (6) contains one or more turns of wire, or smaller winding sections connected in series or parallel. A single turn of a wire has a directional vector d6 that is perpendicular to the area enclosed by the turn. It has also angular span e6 as shown on Figure 2., namely the angular span (e6) is an angle between regions of the winding section (6): (601) and (602), wherein the angle is measured from the axis of rotation. The regions of winding section (601) and (602) are portions of winding section (6) that are parallel to the axis of rotation in an electric rotary machine of a radial geometry, or that are radial in an electric rotary machine of an axial geometry. All turns belonging to the same winding section have the same directional vector d6 and angular span e6. In the real word, directional vectors, or angular spans of different turns are never exactly the same due to imperfections, but all turns belonging to a winding section have the same placement, angular span and directional vector within required level of tolerance. A winding section (6) has two terminals: a positive terminal (35) and a negative terminal (36) of the winding section (6). The convention that we are going to use in this disclosure is that if electric current flows into the positive terminal (35) of a winding section (6) the resulting magnetic field points into the airgap. For winding sections whose angular span (e) is 180 degrees, the choice is arbitrary.

On subsequent Figures in this disclosure, we use a symbol for a winding section (6) as presented on Figure 2 b). Note that on the symbol of a winding section (6), terminals of winding section (35), (36) are placed such that they indicate the angular span e6.

On Figure 2 we present a winding section (6) wounded on rotor core (22), but same symbols and parameters like directional vector d6 or angular span e6 apply for winding sections wounded on stator core (12).

The electric rotary machine might have a radial or axial geometry. For radial geometry, the rotor (2) might rotate inside the stator (1) or outside the stator (1).

Fig. 3 presents a magnetic field extending in stator and rotor.

Electric currents flowing through stator windings (51), or rotor windings (41) cause magnetic field (3), whose lines extend through stator (1) and rotor (2) according to Amper's law and magnetic properties of stator core (12) and rotor core (22).

If one takes a measurement of the magnetic field (3) within the airgap (14) region along a perimeter of a circle whose midpoint is at the axis of rotation, at a given moment of time, the magnetic field (3) at certain place has maximum magnitude, then changes sign, has minimum, changes sign, etc. The number of how many times the magnetic field changes sign when running through the perimeter of the circle is the number of poles of the magnetic field. The magnetic field (3) presented on Figure 2a has four poles. Number of poles in a rotary machine is always even. In this disclosure we use a term "magnetic pole-pairs" and the quantity of magnetic pole-pairs m is the number of magnetic poles divided by two. In case of a real machine, the spatial distribution of the magnetic field might be distorted by local geometry of stator or rotor teethes, therefore one might have to apply spatial filtering in order to filter out those local disturbances and get the proper number of polepairs.

For sake of simplicity on subsequent Figures in this disclosure, we use a symbol of a magnetic field (3) having m pole-pairs as presented on Figure 3 b). Arrows pointing outwards indicate directions where the magnitude of the magnetic field has the highest positive value and arrows pointing inwards indicate directions where the magnetic field has the highest negative value. The quantity of pole-pairs m is the number of arrows divided by two.

A magnetic field might rotate versus stator coordinates XY. For example, if currents through stator windings (51),.., or rotor windings (41),.. change in a proper way, they can cause the magnetic field to rotate. The magnetic field (3) presented on Figure 3 b) rotates in stator coordinates (XY) at angular velocity of W1 . Note, that if the rotor (2) rotates versus stator (1) at angular velocity of WR, the same magnetic field (3) will rotate in rotor coordinates (X'Y) at angular velocity of W1- WR.

The key aspect of this disclosure is that more than one magnetic field can be present in the stator (1) and rotor (2), so the overall magnetic field can be a superposition of its components. Specifically, there might be two components: the first magnetic field (31) and the second magnetic field (32), as it is presented on Figure 3 c). The first magnetic field has m=2 pole-pairs and the second magnetic field has n=3 polepairs. The first magnetic field rotates versus stator coordinates at angular velocity of W1 and the second magnetic field rotates versus stator coordinates XY at angular velocity W2.

The magnetic field can be measured either by at least one magnetic sensor placed in airgap. Well known Hall sensor can be used for this purpose. Another possibility is to measure voltage induced by rotating magnetic field between terminals of windings in the stator or the rotor.

Fig. 4 presents voltages induced between terminals of winding sections by a rotating magnetic field.

Presented on Figure 4 are two winding sections (61) and (62), whose directional vectors d61 and d62 make an angle of 90 degree and a magnetic field (3) having m=3 pole-pairs. The magnetic field (3) rotates versus the winding sections (61), (62) at an angular velocity of W1. According to Faraday's law, the rotating magnetic field will cause AC voltage between positive terminal (35) and negative terminal (36) of each winding section (61), (62). The AC voltage can be graphically represented as a voltage phasor V61 and V62 for each winding section (61) and (62) respectively. Each voltage phasor will rotate at angular velocity of W1 multiplied by quantity of pole-pairs of the magnetic field m. It is so, because per one revolution of magnetic field (30), the induced AC voltage has m maxima and m minima. It is also important, that the relative phase of V61 and V62 is the angle between directional vectors of d61 and d62 multiplied by number of pole-pairs of magnetic field m, in our case 90 degrees * 3 = 270 degrees.

If a winding section (63) is electrically shorted, the voltage induced by changing magnetic field is balanced by electric current induced in the winding section times the resistance of the winding section. Therefore, the current phasor I63 is parallel to the voltage phasor V63 that would be induced if the winding section (63) would hypothetically be open.

Fig. 5 presents voltages and currents induced by two rotating magnetic fields in stator winding composed of two winding sections electrically coupled in a parallel manner.

A stator winding (51) is composed of k=2 winding sections (61) and (62) electrically coupled in a parallel manner in such a way that positive terminals of all winding sections (35) are electrically coupled to the first terminal of the stator winding (71) and negative terminals of all winding sections (36) are electrically coupled to the second terminal of stator winding (72). The first and second terminal of stator winding (71), (72) are electrically coupled to a single-phase AC electric power supply (13) having angular velocity WS.

There are two rotating magnetic fields: a first magnetic field (31) having m=2 pole-pairs and rotating at angular velocity of W1 versus stator coordinates XY and a second magnetic field (32) having n=1 pole-pairs and rotating at angular velocity of W2 versus stator coordinates XY. The first magnetic field (31) is synchronized with the AC electric power supply (13): WS=W1*m, so the voltages induced by first magnetic field in winding sections (61) and (62): V61 and V62 balance the voltage of the AC electric power supply (13). The voltage induced by the second magnetic field (32) within winding sections (61), (62) cannot be compensated by the AC electric power supply, because angular velocity of induced voltage phasors: n*W2 is different than WS. Therefore, from AC perspective, the AC electric power supply (13) represents a short at an angular speed of n*W2 and the second magnetic field (32) induces electric currents in winding sections: 161 and I62 in winding sections

(61) and (62) respectively, as if the winding sections had been electrically shorted.

The voltage phasors generated by first magnetic field (31) in winding sections (61) and (62): V61 and V62 are aligned, because phase difference between V61 and V62 is m*180degrees = 360 degrees. On the other hand, current phasors generated by the second magnetic field (32) in winding sections (61) and (62): 161 and I62 compensate each other, because their phase difference is: n *180 degrees = 180 degrees. It means that electric current induced by the second magnetic field (32) circulates in a circuit formed by the winding sections (61) and

(62) and in an ideal case no current generated by second magnetic field is injected into AC electric power supply (13).

This method of non-injecting any asynchronous current into the AC electric power supply (13) can be generalized for any number of winding sections k, any number of pole-pairs of the first magnetic field m and any number of pole-pairs of the second magnetic field n. The necessary condition for compensation of currents generated by the second magnetic field (32) is that n is not divisible by k. In other words, when dividing n by k there must be a non-zero reminder, for example 7/3, 1/8, 5/4 etc. It is so, because if n would be divisible by k, then currents generated by the second magnetic field in winding sections would be aligned and the result would be an asynchronous AC current injected into the AC electric power supply (13).

The necessary condition for the first magnetic field (31) to generate in- phase voltages at k winding sections whose directional vectors are equally distributed is that m is divisible by k. In other words, m divided by k gives a zero reminder, for example 2/2, 4/2, 5/5 etc.

Practically the current compensation will never be perfect: due to differences in geometry, material properties, or temperature between winding sections, induced currents in winding sections will be slightly different and a fraction of current induced by the second magnetic field (32) will be injected into the AC electric power supply (13). That fraction can be made arbitrarily small by tightening tolerances of the electric rotary machine.

Fig. 6 presents another example of voltages and currents induced in stator winding composed of four winding sections by two rotating magnetic fields.

Figure 6 presents a slightly more complex example of the principle outlined on Figure 5. A stator winding (51) consists of k=4 winding sections: (61), (62), (63) and (64) electrically coupled in a parallel manner in such a way that positive terminals (35) of all winding sections are electrically coupled together to the first terminal of stator winding (71) as well as negative terminals (36) of all winding sections are electrically coupled together to the second terminal of stator winding

(72). The terminals of stator winding (71), (72) are electrically coupled to the AC electric power supply (13).

The magnetic field comprise the first magnetic field (31) having m=4 pole-pairs and rotating at W1 and the second magnetic field (32) having n=3 pole pairs and rotating at W2. The first magnetic field (31) is synchronized with the AC electric power supply (13): W1*m=WS.

Since m=4 is divisible by k=4: 4/4=1 , voltage phasors V61 , V62, V63, V64 are aligned as their phase difference is 90 degrees * 4 = 360 degrees. Since n=3 is not divisible by k=4, current phasors generated by the second magnetic field (32) in different winding sections: 161 , I62, I63, and I64 point symmetrically in different directions and currents get compensated and in an ideal case of a perfect symmetry of winding sections, no current at angular speed of 3*W2 is injected into the AC electric power supply (13). The phase difference between current phasors is 90 degrees * 3 = 270 degrees.

Fig. 7 presents an embodiment where winding sections electrically coupled in a parallel manner are arranged to form a three-phase stator windings.

The stator comprises three stator windings: a first stator winding (51), a second stator winding (52) and a third stator winding (53). Each stator winding contains two winding sections. The first stator winding (51) contains k=2 winding sections: (61) and (62) electrically coupled in a parallel manner. The second stator winding (52) contains k=2 winding sections: (63) and (64) electrically coupled in a parallel manner. The third stator winding (53) contains k=2 winding sections: (65) and (66) electrically coupled in a parallel manner. The three stator windings (51), (52) and (53) are arranged in a delta configuration.

There are two rotating magnetic fields: first magnetic field (31) having m=2 pole-pairs and the second magnetic field (32) having n=3 polepairs. Since for each stator winding the angle between directional vectors of winding sections is 180 degrees and m=2, the phase difference between induced voltages is 2 * 180 degrees = 360 degrees.

At the angular speed related to the second magnetic field, the winding sections are effectively shorted, therefore we consider currents induced by the second magnetic fields. Since k=2 and n=3, the phase difference between 161 and I62 is 3 * 180 degrees -> effectively 180 degrees and currents cancel each other and no current flows to the AC electric power supply (13). The same applies for other windings consisting of pairs: (63), (64) and (65), (66).

The angle between directional vectors of winding sections belonging to different stator windings is 60 degrees: (61) and (65) or -60 degrees between (61) and (63). Therefore, the phase difference between V61 and V65 is m*60degrees=120 degrees. Similarly, the difference between V61 and V63 is -120 degrees. Therefore, terminals of stator windings can be electrically coupled to a three phase AC electric power supply (13), where phase differences are 120 degrees and -120 degrees. On Figure 7 a delta connection of stator winding is presented. The Figure 7 presents in detail how terminals of winding sections are electrically coupled to each other and to 3 phases of AC electric power supply (13). For the sake of clear illustration, a connection by name convention is used, where names of nodes are: a, b and c.

On Figure 7, the first terminal of first stator winding is electrically coupled to node b, the second terminal of first stator winding is electrically coupled to node a, the first terminal of the second stator winding is electrically coupled to node c, the second terminal of the second stator winding is electrically coupled to node b, the first terminal of the third stator winding is electrically coupled to node a and the second terminal of the third stator winding is electrically coupled to node c.

Fig. 8 presents voltages and currents induced by two rotating magnetic fields in stator winding composed of two winding sections electrically coupled in an anti-parallel manner.

A stator winding (51) is electrically coupled to the AC electric power supply (13). The stator winding (51) comprises k=2 winding sections: a first winding section (61) and a second winding section (62). The winding sections are electrically coupled in an anti-parallel manner: the negative terminal (36) of the first winding section (61) and the positive terminal (35) of the second winding section (62) are electrically coupled to the first terminal of the stator winding (71). The positive terminal (35) of the first winding section (61) and the negative terminal (36) of the second winding section (62) to the second terminal of the stator winding (72).

There are two rotating magnetic fields: a first magnetic field (31) having m=1 pole-pairs and rotating at angular velocity of W1 and a second magnetic field (32) having n=2 pole pairs and rotating at angular velocity of W2. The first magnetic field (31) is synchronized with the AC electric power supply (13): WS=W1*m, so the voltages induced by first magnetic field in winding sections (91) and (92): V61 and V62 balance the voltage of the AC electric power supply (13). The phase difference between V61 and V62 is 180 degrees, but since winding sections (61) and (62) are electrically coupled in anti-parallel manner, they both balance the voltage of the AC electric power supply (13).

The voltage induced by the second magnetic field (32) within winding sections (61), (62) cannot be compensated by the AC electric power supply, because angular speed of n*W2 is different than WS. Therefore, from AC perspective, the AC electric power supply represents a short at angular speed of n*W2 and the second magnetic field (32) induces electric currents in winding sections: 161 and I62 as if the winding sections had been electrically shorted. Since n=2 and the angle between directional vectors of the winding sections is 180 degrees, the phase difference between 191 and I92 is 360 degrees. Now, because of the anti-parallel connection of the two winding sections (61) and (62), currents 161 and I62 compensate each other, and in ideal case no current generated by the second magnetic field (32) flows into the AC electric power supply (13).

Note that the principle of compensating currents induced by the second magnetic field (32), so they don't flow to the AC electric power supply (13), had not worked for k=2, m=1 and n=2 if the winding sections (61) and (62) would be electrically coupled in a parallel manner like on Figure 5.

In a general case of any quantity of k, m, n, the necessary conditions for this principle to work are: k must be divisible by 2, because half of k winding sections is electrically coupled in a parallel and another half in an anti-parallel manner so half of k must be a natural number, not a fraction. n must be divisible by k, so the currents induced by the second magnetic field (32) in all k winding sections are in phase - in other words phase difference between induced currents in different winding section is a multiplicity of 360 degrees. Now, since half of all k winding sections are electrically coupled in a parallel manner and the other half in anti-parallel manner, all those currents compensate each other, and no currents induced by the second magnetic field flows into the AC electric power supply (13). m must not be divisible by k and 2*m must be divisible by k. In that way the phase difference of voltages induced at any consecutive winding sections is 180 degrees. As consecutive windings are electrically coupled in an anti-parallel manner, it means that voltage induced at any winding section can compensate the voltage provided by the AC electric power supply.

Winding sections belonging to one stator winding are numbered sequentially according to the angle between the directional vector of each winding section and X-axis. The purpose is that every second winding section is electrically coupled in parallel, and every other winding section is electrically coupled in anti-parallel manner.

Fig. 9 presents an embodiment where winding sections electrically coupled in an anti-parallel manner are arranged to form a three-phase stator windings.

The stator comprises three stator windings: a first stator winding (51), a second stator winding (52) and a third stator winding (53). Each stator winding contains two winding sections. The first stator winding (51) contains k=2 winding sections: (61) and (62) electrically coupled in antiparallel manner. The second stator winding (52) contains k=2 winding sections: (63) and (64) electrically coupled in an anti-parallel manner. The third stator winding (53) contains k=2 winding sections: (65) and (66) electrically coupled in an anti-parallel manner. The three stator windings (51), (52) and (53) are arranged in a star configuration, such that the first terminal of every stator winding is electrically coupled to a three-phase AC electric power supply (13) and all second terminals of every stator winding are electrically coupled together to a common node b.

There are two rotating magnetic fields: first magnetic field (31) having m=1 pole-pairs and the second magnetic field (32) having n=2 polepairs. Since for each stator winding the angle between directional vectors of winding sections is 180 degrees and m=1 , the phase difference between induced voltages is 1 * 180 degrees = 180 degrees.

At the angular speed related to the second magnetic field: W2, the winding sections are effectively shorted, therefore we consider currents induced by the second magnetic fields. Since k=2 and n=2, the phase difference between 161 and I62 is 2 * 180 degrees -> effectively 0 degrees and because of anti-parallel connection, currents cancel each other and no current flows to the AC electric power supply (13). The same applies for other windings consisting of pairs: (63), (64) and (65), (66).

The angle between directional vectors of winding sections belonging to different stator windings is 60 degrees: (61) and (65) or -60 degrees between (61) and (63). Therefore, the phase difference between V61 and V65 is m*60degrees=60 degrees. At the same time due to antiparallel connection, the effective voltage at terminals of winding (53) is shifted by 180 degrees + 60 degrees -> -120 degrees versus voltage at terminals of winding (51). Similarly, the difference between V61 and V63 is -60 degrees. Again, because of anti-parallel connection of (63), the effective voltage at terminals of winding (52) is shifted by 180 degrees - 60 degrees -> 120 degrees versus voltage at terminals of winding (51). Therefore, terminals of stator windings can be electrically coupled to a three phase AC electric power supply (13). The Figure 9 presents in detail how terminals of winding sections are electrically coupled to each other and to a 3 phase AC electric power supply (13).

Fig. 10 presents a rotor current distribution.

Figure 10 a) presents a rotor (2) comprising two winding sections (61) (62). Each winding section has a positive terminal of a winding section (35) and a negative terminal of a winding section (36).

Figure 10 b) presents a cross section of the rotor (2). In this example the electric rotary machine has radial geometry. The cut for the crosssection is done along a plane that is perpendicular to the axis of rotation. For an electric rotary machine having an axial geometry an analogous cut can be made along a cylinder whose axis is the axis of rotation. The cross-section cuts winding sections (61) and (62) in four regions: (R61), (R62), (-R61) and (-R62). The region (R61) is where currents in winding section (61) flow in one direction and the region (- R61) is where those currents return. Similarly, for (62). The value of 161 is the value of entire current flowing though marked region (R61). It is the area integral of current density in that region, or the sum of all currents flowing through all turns that cross the region. The sum of 161 and -161 is zero. Similarly, for (62).

The rotor current distribution (IR) is a function that assigns to every region where the rotor cross section cuts winging sections a value of entire current flowing through that region. The rotor current distribution IR is graphically shown on Figure 10c.

If rotor current distribution (IR) is presented graphically for all regions ordered sequentially as they are ordered in the rotor, then the chart has minima and maxima. The number of how many times the chart of IR crosses zero is the number of magnetic poles the IR generates. For the magnetic field generated by IR on Figure 10c there are two zerocrossings, so there are: m=1 pole-pairs.

The rotor current distribution IR might rotate at certain angular velocity W3 in rotor coordinates X'Y'. To achieve that effect, currents in different winding sections (61), (62) change. On the graphical representation like the one shown on Figure 10c, rotation of rotor current distribution at angular velocity of W3 versus rotor coordinates is equivalent to moving the chart of IR vertically at speed of W3, if the vertical span of the chart of IR is 2 * pi = 6.28...

The rotor current distribution (IR) can be measured by measuring electric currents in every winding section belonging to the rotor and multiplying it by number of turns belonging to every section.

The rotor current distribution (IR) can be a superposition of plurality of components. It can comprise components IR1 , IR2 having different number of pole-pairs and rotating at different angular speeds. Furthermore, a component of rotor current distribution has certain magnitude and phase like any periodic function. The magnitude or phase of rotor current distribution can be controlled by applying currents in rotor winding sections.

Fig. 11 presents an embodiment of a rotor winding and rotor power switches for regulating electric current in the rotor winding.

Figure 11 presents a rotor winding (41) having two terminals of rotor winding (8), each terminal electrically coupled to two rotor power switches: a first rotor power switch (91) and a second rotor power switch (92). The first rotor power switch (91) has the other terminal electrically coupled to the positive terminal of the rotor DC supply (28) and the second rotor power switch (92) has the other terminal electrically coupled to the negative terminal of the rotor DC supply (29). This is a bridge configuration of a winding (4) and by regulating states of the four rotor power switches, one can control the value of the electric current flowing through the winding. The most common control method is the PWM method.

The relay (900) is a device that can be in open state, or closed state. In open state, the electric current flowing through the relay (900) is insignificant, very close to zero. In the closed state, the resistivity of the relay (900) is small, so current can flow. The relay is electrically coupled to the winding (41) in such a way, that if the relay is in open state, no electric current will be allowed to flow through the winding (41). On Figure 11 , the winding (41) and the relay (900) are connected in series. The relay is closed in normal operation, and only in a fault condition it is opened. By fault conditions we mean a breakdown of one of rotor power switches (91) or (92), or breakdown of an isolation of the winding (41). If any of those fault conditions is detected, the relay (900) is put into open state and all switches (91) or (92) are driven to be open by a switch driver (20). Therefore, despite of the fault, no uncontrolled current flows: neither through power switches (91), (92), nor through the winding (41).

Fig. 12 presents an embodiment of rotor windings to generate two magnetic fields rotating independently and a corresponding rotor current distribution.

The rotor comprises eight rotor windings (41), (42), ... (48). Each rotor winding comprises only a single winding section having angular span of 180 degrees. All windings have directional vectors equally distributed. Each rotor winding is electrically coupled to rotor power switches (9) in a full bridge arrangement, like explained in detail on Figure 11. PWM control can be applied for the rotor power switches in order to regulate current of each rotor winding (41), ..,(48) independently from currents in other rotor windings.

The goal of the embodiment presented on Figure 12 is to generate two rotating magnetic fields: the first magnetic field (31) having m=3 polepairs and the second magnetic field (32) having n=1 pole-pair. The first magnetic field (31) is supposed to rotate at angular speed of W1-WR in rotor coordinates X'Y', wherein WR is the angular rotation speed of the rotor. In that way the first magnetic field (31) rotates at angular speed of W1 versus stator coordinates XY. The second magnetic field (32) rotates in the opposite direction at angular speed of W2 + WR versus rotor coordinates X'Y', what transforms to an angular speed of W2 in stator coordinates XY. This goal is achieved by regulating rotor current distribution IR to be a sum of two components: IR1 and IR2. The first component IR1 has m=3 pole-pairs and rotates at angular speed of W1- WR in rotor coordinates. The second component IR2 has n=1 pole-pairs and rotates at angular speed of W2 + WR. Currents through each individual rotor winding is regulated to be a sum of current in this rotor winding according to IR1 plus current in this rotor winding according to IR2.

A component of rotor current distribution IR1 , or IR2 has the same number of pole-pairs and rotates at the same angular speed as the magnetic field (31), (32) the component generates.

There is however a condition imposed on quantity of pole-pairs of first magnetic field m, quantity of pole-pairs of the second magnetic field n and angular span e of rotor winding section for this principle to work. Namely, the angular span e of each winding section must correspond to 180 electrical degrees in both: m pole-pair system as well as in n-pole- pair system. It is so, because after e mechanical degrees, the current changes phase by 180 degrees. Mathematically it corresponds to a requirement that there must exist a natural number p such that: e*n = 180 degrees + p*360 degrees. At the same time there must exist a natural number q such that: e*m = 180 degrees + q*360 degrees. Natural numbers p and q can be any of: 0, 1 , 2... It corresponds to a requirement that: n - m = 2*(p*m - q*n). A consequence of this requirement is that not every pair of (m,n) can be realized using this principle. Another result is that e = 180 degrees*(1 + 2*q) I m. For the example on Figure 12, with m=3 and n=1 , p = 0 and q = 1. Fig. 13 presents a how an arrangement, where magnetic fields having two components can be generated by two types of rotor windings in such a way that the first magnetic field doesn't induce voltage in the second type of rotor windings and the second magnetic field doesn't induce voltage in the first type of rotor winding.

The rotor comprises two rotor windings (41) and (42). The first rotor winding (41) belongs to the first type of rotor windings. The second rotor winding (42) belongs to the second type of rotor windings. For the sake of clear illustration, they are shown separately on Figure 13, but in a real rotor they are wound on the same rotor core (13). The first rotor winding (41) belonging to a first type of rotor windings comprises m=3 winding sections: (61), (62) and (63). The second rotor winding (42) belonging to the second type comprises n=2 winding sections: (64) and (65). Winding sections of each winding type are electrically coupled in series taking into account the polarity of connections, so the current flows in the same direction in every winding section: for example, from positive terminal to negative terminal in every winding section, or from negative terminal to the positive terminal in every winding section.

The aim of the embodiment presented on Figure 13 is to generate two rotating magnetic fields: first magnetic field (31) having m=3 pole-pairs and the second magnetic field (32) having m=2 pole-pairs and fulfill following conditions: rotor winding (41) belonging to the first type generate first magnetic field (31) rotor winding (42) belonging to the second type generate second magnetic field (32) voltage induced by the first magnetic field (31) on windings belonging to the second type (42) is zero voltage induced by the second magnetic field (32) on windings belonging to the first type (41) is zero.

If electric current flows through the first rotor winding (41), the first rotor winding (41) generates the first magnetic field (31) having m=3 polepairs. If electric current flows through the second rotor winding (42), the second rotor winding (42) generates the second magnetic field (32) having n=2 pole-pairs.

Let's now consider voltages induced in winding sections. If the first magnetic field (31) rotates versus rotor coordinates X'Y', it will induce voltages V61_1 , V62_1 , V63_1 in winding sections (61), (62) and (63) respectively. The second magnetic field (32) will induce voltages V61_2, V62_2 and V63_2. Similarly for the second winding (42): the first magnetic field (31) induces voltage V64_1 , V65_1 in winding sections (64) and (65) respectively and the second magnetic field (32) induces voltages V64_2 and V65_2.

The voltages generated by the first magnetic field (31) in winding sections belonging to first winding (41) add up: V41_1=V61_1+V62_1+V63_1. It is so, because the phase between V61_1 and V62_1 is equal 120 degrees * m = 360 degrees. The same is true for voltages generated by the second magnetic field (32) in winding sections belonging to the second winding (42): V42_2=V64_2 + V65_2, because the phase between V64_2 and V65_2 is equal 180 degrees * n = 360 degrees.

The voltages generated by the first magnetic field (31) in winding sections belonging to the the second winding (42) cancel each other, because the phase between V64_1 and V65_1 is equal 180 degrees * m = 540 degree -> effectively 180 degrees. The same is true for voltages generated by the second magnetic field (32) in winding sections belonging to the first winding (41). They cancel each other: V61_2+ V62_2+V63_2=0 because phase difference is 120 degrees * n = 240 degrees, so we have three symmetrical phasors, whose sum is zero.

In a general case of any quantity of m, n, the necessary conditions for this principle to work are: the first type of rotor winding contains m winding sections electrically coupled in series, the second type of rotor winding contains n winding sections electrically coupled in series, m is not divisible by n, n is not divisible by m.

Fig. 14 presents an embodiment of the electric rotary machine.

The electric rotary machine comprises a stator (1) and a rotor (2). The stator (1) comprises three stator windings: (51), (52) and (53). Every stator winding contains k=3 winding sections, equally distributed, so directional vectors of winding sections belonging to the same winding make an angle of 120 degrees. Terminals of k winding sections are electrically coupled in a parallel manner. Stator windings (51), (52) and (53) are electrically coupled in a delta configuration to nodes a, b and c as shown on the Figure 14. For operation of the electric rotary machine, nodes a, b, and c are electrically coupled to a three-phase AC electric power supply (13) having angular velocity of WS. The rotor comprises eight rotor windings (41), (42)..., and (48). Each rotor winding consists of a single winding section. Each winding section has an angular span of 180 degrees. The winding sections are equally distributed, so the angle between directional vector of two consecutive rotor windings is 22.5 degrees.

The rotor further comprises a rotor DC supply (21) implemented by a capacitor and 32 rotor power switches (9) implemented by power FETs. The rotor DC supply has a positive terminal of rotor DC supply (28) and a negative terminal of rotor DC supply (29). During operation of the electric rotary machine, the voltage at the positive terminal of rotor DC supply (28) is higher than the voltage at the negative terminal of rotor DC supply. For every terminal of rotor winding (41), ... (48) there is one rotor power switch (9) electrically coupling the terminal to the positive terminal of rotor DC supply (28) and one power switch (9) electrically coupling the terminal to the negative terminal of rotor DC supply (29).

A rotor controller (24) is electrically coupled to gates of rotor power switches (9) and is configured to control states of rotor power switches (9). The rotor controller (24) can control current through every rotor winding (41)..., (48) individually by switching terminals of the winding between terminals of rotor DC supply: (28) and (29) in a PWM scheme.

The rotor further comprises a rotor communication unit (25) configured to receive or transmit information, so the function of the rotor controller (24) can be supervised by other devices or humans and information about status of the electric rotary machine or fault monitoring data can be send back from the rotor controller (24). Electric currents flowing through rotor windings (41)...(48) result in rotor current distribution IR having two components: IR1 and IR2. The first component IR1 has m=3 pole-pairs and rotates versus rotor coordinates at angular velocity of WS/m -WR in counter-clockwise direction, wherein WR is the angular velocity of the rotor (2) versus the stator (1). The second component IR2 has n=1 pole-pairs and rotate versus rotor coordinates at angular velocity of W2+WR in clockwise direction.

The rotor current distribution IR generate magnetic field extending in stator (1) and rotor (2), the magnetic field comprising a first magnetic field (31) and a second magnetic field (32). The first magnetic field, generated by first component IR1 , has m=3 pole-pairs and is synchronized with the AC electric power supply (13), therefore rotating at angular speed of W1=WS/m counter-clockwise in stator coordinates XY. The second magnetic field, generated by the second component IR2, has n=1 pole-pairs and rotates at angular speed of W2 clockwise versus stator coordinates XY. For high efficiency of the electric rotary machine, the absolute value of W2 is smaller than one fifth of the absolute value of W1 .

Because of parallel connection of winding sections in each stator winding (51), (52), (53), currents generated by the second magnetic field (32) in those winding sections cancel and no asynchronous current is injected into AC electric power supply (13).

For every stator winding, or rotor winding, there is an average electric power of the winding. The average electric power of a winding is an average value of a product of voltage across terminals of the winding times current of the winding. The average electric power of rotor windings PR is a sum of average electric power of each rotor winding. Similarly, the average electric power of stator windings PS is a sum of average electric power of each stator winding.

If the rotor current distribution IR is a sum of two components: IR1 and IR2, it means that current of every winding is a sum of two currents: first being part of IR1 and second being part of IR2. Therefore, the average electric power of rotor windings PR is also a sum of two components: PR1 + PR2, wherein the first component PR1 is related to the first component of rotor current distribution IR1 and the second component PR2 is related to the second component of rotor current distribution IR2.

During a steady state operation of the electric rotary machine, PR1 and PR2 have opposite signs and almost cancel out, the small remaining power PR=PR1+PR2 might be used to power rotor parts like rotor controller, rotor power switches and rotor communication unit. Therefore, the absolute value of average electric power of rotor windings: |PR| is typically significantly smaller than the absolute value of average electric power of stator windings: |PS|. In an ideal case, where heat losses, or power of rotor parts is zero, entire PS is converted to mechanical power PM and PR is equal zero.

On Figure 14 arrows of PS, PR1 , PR2, PR, PM indicate direction of power flow into or out of the electric rotary machine in a generator mode.

To analyze power flow within the electric rotary machine, we take the average electric power and not instantaneous electric power, because due to AC signals, instantaneous electric power might change versus time, while in steady state type of operation, the average electric power is constant. Fig. 15 presents an embodiment of the electric rotary machine comprising compensation of harmonic currents and vibrations.

Additionally to the electric rotary machine presented on Figure 14, the stator (1) further comprises current sensors (37) configured to measure currents flowing at AC supply connections (27). Currents might be measured using one of known methods, like shunt resistors, Hall sensors, current transformers, or others. From the information delivered from current sensors (37), angular velocity (that is 2*pi*frequency), magnitude and phase of harmonic currents injected into the AC electric power supply (13) might be extracted.

Additionally to the electric rotary machine presented on Figure 14, the rotor (1) further comprises a vibration sensor (39) attached to the shaft (23) and configured to measure mechanical vibrations due to time variation of torque. Vibrations might be measured using one of known methods, like accelerometer, position sensor, vibrometer, or other. From the information delivered from the vibration sensor (39), angular speed, magnitude and phase of vibrations might be extracted.

For reduction of undesired currents injected into the AC electric power supply (13), the rotor current distribution IR comprises at least one component IRh having h=3 pole-pairs and rotating versus rotor coordinates at Wh+WR. Therefore it rotates versus stator coordinates at an angular velocity of Wh. The component IRh results in harmoniccompensating magnetic field (33) also having h=3 pole-pairs and rotating versus stator coordinates at angular velocity of Wh.

Consider as an example, that the undesired current injected into the AC electric power supply has an angular speed of 2*WS+3*WII resulting from fifth order mixing between first magnetic field (31) and second magnetic field (32). The harmonic-compensating magnetic field (33) has than angular velocity Wh equal (2*WS+3*WII)/h and rotating in the opposite direction to WS. Since h=3 is divisible by quantity of winding sections in a stator winding k=3, the harmonic-compensating magnetic field (33) will induce currents in parallel-connected winding sections resulting in net current at terminal of every winding section at an angular velocity of 2*W2+3*WII. The induced current is supposed to cancel the original undesired current injected into the AC electric power supply at the same angular velocity.

For reduction of vibrations, the rotor current distribution IR comprises at least one component IRv having v=1 pole-pairs and rotating versus rotor coordinates at Wv+WR. Therefore, it rotates versus stator coordinates at an angular velocity of Wv. The component IRv results in vibration-compensating magnetic field (34) also having v=1 pole-pairs and rotating versus stator coordinates at angular velocity of Wv.

Fig. 16 presents a stator winding as a serial connection of winding groups.

The stator winding (51) has two terminals of stator winding (71), (72) and consists of three winding groups (500) connected in serial manner, each winding group (500) consisting of a quantity of k=4 winding sections (61), (62), (63), (64) connected in a parallel manner.

The k winding sections (61), (62), (63), (64) in each winding group (500) are arranged in such a way, that electric currents induced by the second magnetic field (32) cancel each other, so in ideal conditions no current induced by the second magnetic field (32) flows through terminals of stator winding (71), (72).

Fig. 17 presents an electric power generation system, wherein the electric rotary machine is driven by a prime mover to generate electricity.

A prime mover (26) is mechanically coupled to the electric rotary machine (11) by a shaft (23). The prime mover might be a wind turbine, a steam turbine, a water turbine, a gas turbine or a combustion engine, or other device. The electric rotary machine (11) is electrically coupled to the 3 phase AC electric power supply (13) through AC supply connections (27). The electric power generation system can transform mechanical power PM delivered from the prime mover (26) into electrical power delivered to the AC electric power supply (13).

LIST OF REFERENCE NUMERALS AND SYMBOLS

1 stator

11 electric rotary machine

12 stator core

13 AC electric power supply

14 airgap

2 rotor

21 rotor DC supply

22 rotor core

23 shaft

24 rotor controller

25 rotor communication unit

26 prime mover

27 AC supply connection

28 positive terminal of rotor DC supply

29 negative terminal of rotor DC supply

3 magnetic field

31 first magnetic field

32 second magnetic field

33 harmonic-compensating magnetic field

34 vibration-compensating magnetic field

35 positive terminal of a winding section

36 negative terminal of a winding section

37 current sensor

39 vibration sensor

41 , 42,... 48 rotor winding

51 , 52, 53, 54 stator winding 500 winding group

6, 61 , 62, ..., 66 winding section

601 , 602 region of a winding section

7, 71 , 72 terminal of stator winding

8, 81 , 82 terminal of rotor winding

9, 91 , 92 rotor power switch

900 relay a, b, c, d names of electrical nodes d6, d61 , d62, d63 directional vector of a winding section (respectively) e, e6, e61 , e62, e63 angular span of a winding section (respectively) f quantity of phases of the AC electric power supply h quantity of magnetic pole-pairs of the harmonic-compensating magnetic field

I6, 161 , I62, I63 current induced in a winding section (respectively)

PF power factor at the AC electric power supply

IP1 first component of electric current at a terminal of the AC electric power supply

IP2 second component of electric current at a terminal of the AC electric power supply

IR rotor current distribution

IR1 first component of rotor current distribution

IR2 second component of rotor current distribution

I Rh harmonic-compensating component of rotor current distribution

IRv vibration-compensating component of rotor current distribution k quantity of winding sections in a stator winding m quantity of magnetic pole-pairs of the first magnetic field n quantity of magnetic pole-pairs of the second magnetic field p any natural number (0, 1 , 2, 3, ...) q any natural number (0, 1 , 2, 3, ...)

PM mechanical power of electric rotary machine PR average electric power at rotor windings

PR1 first component of average electric power at rotor windings

PR2 second component of average electric power at rotor windings

PS average electric power at stator windings

R61 , R62 regions where winding sections (respectively) cross a rotor cross section

-R61 , -R62 regions where winding sections (respectively) cross a rotor cross section in return path

R41 , R42 .. regions, where rotor windings (respectively) cross a rotor cross section

T torque v quantity of magnetic pole-pairs of the vibration-compensating magnetic field V41_1 , V42_1 voltage induced in a rotor winding by the fist magnetic field

V41_2, V42_2 voltage induced in a rotor winding by the second magnetic field

V6, V61 , V62, V63 voltage induced in winding section (respectively)

V61_1 , V62_1 , ... voltage induced in a winding section (respectively) by the first magnetic field

V61_2, V62_2, ... voltage induced in a winding section (respectively) by the second magnetic field

W1 angular velocity of the first magnetic field in stator coordinates

W2 angular velocity of the second magnetic field in stator coordinates

W3 angular velocity of a magnetic field in rotor coordinates

Wh angular velocity of the harmonic-compensating magnetic field in stator coordinates

WR angular velocity of the rotor in stator coordinates

WS angular velocity of the AC electric power supply

Wv angular velocity of the vibration-compensating magnetic field in stator coordinates

XY stator coordinates

X'Y' rotor coordinates