RU2844074C1 - Electrical machine - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: invention relates to the field of electrical equipment, electrical machines, in particular to electrical machines with excitation winding on the rotor. Electric machine contains stator magnetic circuit with 2p-pole three-phase winding connected into star, zero-sequence harmonic injector connected to common point of stator winding, salient-pole rotor with slots located with pitch of 180/p degrees, where excitation winding is laid. Rotor comprises also harmonic exciter winding, rectifier with DC outputs connected to excitation winding and AC outputs connected to harmonic exciter winding. At that, all slot sides of harmonic exciter winding are laid into slots located on rotor teeth, and harmonic exciter winding has two or more phases.

EFFECT: enabling the machine starting and excitation possibility at the rotor any position, eliminating the hysteresis current controller, eliminating the harmonic winding parts in the excitation winding slots, as well as improved specific characteristics and efficiency, reduced moment pulsations and vibrations.

11 cl, 13 dwg

Description

The invention relates to electrical machines, in particular to electrical machines with an excitation winding on the rotor, and can be used in electric drives and generator units.

An analogue of the proposed electric machine is a synchronous electric machine with a semiconductor power source, described in patent US 9813004 B2 (title: "Systems and methods concerning exciterless synchronous machines"; authors: Ghanshyam Shrestha, Darren Tremelling, Waqas Arshad, Wen Ouyang, Jan Westerlund, 2017). This system contains an inverter powered by a DC link, connected to a multiphase stator winding of the electric machine. This inverter is designed to transmit alternating current power to the stator winding of the electric machine, including both the fundamental temporary harmonic and the injected harmonics generated by the injector (a special inverter module).

This system also contains a synchronous electric machine, which has:

- a multiphase armature winding on the stator, connected in a star without a midpoint;

- a winding of the harmonic exciter on the rotor (hereinafter, for brevity, simply “harmonic winding”), which can be multi-phase; this winding is constructed in such a way as to accept the energy of the injected harmonics;

- excitation winding on the rotor;

- a direct current source designed to receive the energy of injected harmonics from the winding of the harmonic exciter and supply power to the excitation winding.

Meanwhile, the combination of these features in US 9813004 B2 does not provide sufficient magnetic excitation flux and sufficiently high efficiency of the excitation system, which reduces the efficiency of the synchronous machine as a whole. Also, the inclusion of the stator winding in a star without the midpoint output leads to the presence of an injected component in the fundamental spatial harmonic of the induction in the gap, which leads to an increase in torque pulsations and vibrations. This also leads to the fact that the deviation of the control angle from the value specified by the control system, due to the admixture of the injected harmonic, reduces the efficiency of the machine. In addition, part of the DC link voltage is used by the inverter to create injected harmonics. Therefore, to achieve the same amplitude of the fundamental harmonic voltage, an increase in the DC link voltage is required, and, as a result, an increase in the inverter power is required. In addition, the operation of the electric machine described in patent US 9813004 B2 requires an inverter (active rectifier) in the stator winding circuit, which limits the use of this solution in generator sets with a diode bridge (passive rectifier), as well as in generator sets without a diode bridge.

The closest analogue of the proposed invention is the electric machine described in patent KR20230075074A (title "Single-Inverter-Controlled Brushless Technique for Wound Rotor Synchronous Machines", authors: Noh Jong-seok, Syed Sabir, Hussein Bukhari, 2023), as well as in the article "Brushless Field Excitation Scheme for Wound Field Synchronous Machines" authored by Syed Sabir Hussain Bukhari, Ghulam Jawad Sirewal, Faheem Akhtar Chachar and Jong-Suk Ro published in Applied Sciences (7 August 2020, 10(17):5866, DOI: 10.3390/app10175866). This electric machine is used in conjunction with a hysteresis three-phase current inverter. In this system, zero sequence injection is performed through the common point of the stator winding connected in a star. Each rotor tooth near the gap is divided into two subteeth, onto which a single-phase harmonic winding is wound. As a result, one of the slot sides of the harmonic exciter winding coils fits into the slot of the excitation winding.

In this case, it is also possible to implement the design variant of the electric drive described in the "Brushless Field Excitation Scheme for Wound Field Synchronous Machines", in which the zero-sequence injection is carried out by means of an additional single-phase injector. As a result, the power of the three-phase inverter is reduced. In this case, if the voltage and current required to excite the third harmonic are less than the voltage and current of the fundamental harmonic, lower-current transistors can be used in the injector, which reduces their cost.

In addition, the rotor described in the article "Brushless Field Excitation Scheme for Wound Field Synchronous Machines" is designed to generate torque under the influence of positive sequence. Therefore, the negative impact of the presence of zero sequence is lower than that of the injection components of positive sequence. These factors contribute to the reduction of torque pulsations, as well as to the increase in the efficiency and specific characteristics of the electric machine.

Fig. 1 shows the electric machine described in the article "Brushless Field Excitation Scheme for Wound Field Synchronous Machines" at the moment when the rotor teeth centers are located opposite the axes of the resulting magnetic field of the stator winding phases (hereinafter, for brevity, simply "phase axes"). These axes have no orientation and are rotated along the vector of the resulting magnetomotive force (MMF) formed by the MMF vectors of individual phase coils when in-phase currents flow. Such an axis corresponds to the center of the phase zone. According to Lenz's rule, the current in the harmonic winding tends to demagnetize the zero-sequence magnetic field in the stator winding. This current is rectified and feeds the excitation winding.

Fig. 2 shows the electric machine described in the article "Brushless Field Excitation Scheme for Wound Field Synchronous Machines" at the moment when the rotor teeth centers are located opposite the boundaries of the phase zones of the stator winding. In this case, there are no zero-sequence currents opposite the rotor teeth center, i.e. there is no reason for the induced current to appear in the harmonic winding. Thus, with this rotor position, energy transfer to the excitation winding is impossible. Therefore, starting the machine in the motor mode with this rotor position is also impossible. In intermediate rotor positions, energy transfer to the excitation winding is not effective, which reduces the efficiency of its excitation and leads to a decrease in the efficiency of the synchronous machine as a whole.

This inefficiency of excitation energy transfer is partly compensated by the use of a hysteresis current regulator with a large output resistance, which eliminates the flow of direct or reverse sequence currents with the injection frequency, induced by the EMF arising due to the inevitable interaction of zero-sequence currents with the rotor anisotropy. The hysteresis current regulator requires high-quality current sensors in its design.

In addition, for efficient energy transfer to the harmonic winding, it is necessary that the angular size of the rotor sub-tooth be approximately equal to the pole division of the spatial third harmonic, and the entire rotor tooth be approximately equal to the period of the spatial third harmonic, i.e. approximately 120 electrical degrees. This limits the possibilities of optimizing the design of the synchronous machine and achieving high efficiency and energy characteristics.

In addition, in each slot of the rotor, along with the excitation winding, two slot sides of the turns of the harmonic winding are placed, directed oppositely. However, the spatial change in the z-component of the vector magnetic potential occurs mainly in magnetic circuits, and in non-magnetic media it is practically absent. As a result, the slot sides of the harmonic winding, placed in the slots of the excitation winding, make opposite, balancing contributions to the EMF of the harmonic winding, i.e., they do not lead to any useful effect. Their location in the slot of the excitation winding complicates the design, reduces the space allocated for the excitation winding and, as a result, reduces the efficiency of the machine.

The technical result of the proposed invention consists in the possibility of starting and excitation at any position of the rotor, eliminating the expensive hysteresis current regulator, eliminating parts of the harmonic winding in the slots of the excitation winding that do not provide a useful effect, as well as improving the specific characteristics and efficiency and reducing torque pulsations and vibrations.

The essence of this invention is explained by sketches, which depict:

- Fig. 1 - a known design with zero sequence injection, with a rotor position in which energy transfer to the excitation winding is possible;

- Fig. 2 - a known design with zero-sequence injection, with a rotor position in which energy transfer to the excitation winding is impossible;

- Fig. 3 - an electric machine with a two-phase winding of a harmonic exciter without a common branch;

- Fig. 4 - rotor of an electric machine with a two-phase winding of a harmonic exciter without a common branch;

- Fig. 5 - electrical diagram of the rotor;

- Fig. 6 - options for connecting the stator winding power supply circuit without an inverter (active rectifier): (a) Option without a diode bridge rectifier; (b) Option with a diode bridge rectifier.

- Fig. 7 - electrical circuit of the stator winding power supply with an inverter;

- Fig. 8 - rotor of an electric machine with a two-phase winding of a harmonic exciter, the slot groups of which contain two slots each;

- Fig. 9 - rotor of an electric machine with a two-phase winding of a harmonic exciter with a common branch: (a) sketch of the rotor; (b) electrical circuit of the rotor.

- Fig. 10 - rotor of an electric machine with a two-phase winding of a harmonic exciter with three slots on each tooth of the rotor;

- Fig. 11 - options for connecting compensating capacitors to the winding of the harmonic exciter: (a) Smekha with two capacitors without a common branch; (b) Smekha with three capacitors without a common branch; (c) Smekha with two capacitors with a common branch; (d) Smekha with three capacitors with a common branch.

- Fig. 12 - rotor of an electric machine with slots.

- Fig. 13 - angular distances between groups of slots and phase axes of the winding of a harmonic exciter with a two-phase winding of a harmonic exciter without a common branch.

For further exposition, we will introduce some definitions. By a group of slots of the harmonic exciter winding (hereinafter, for brevity, simply "slot group") we will understand a set of adjacent slots of this winding, located on one tooth of the rotor and belonging to one phase, in which the current of the same direction flows. The middle direction of such a group of slots is determined as follows. The angular position of the slots relative to the middle of the rotor tooth is determined. For definiteness, we will choose the counterclockwise direction as positive. Then the middle direction of the group of slots of the harmonic exciter winding, located on one tooth of the rotor, has an angular position equal to the arithmetic mean of the positions of these slots.

Similarly, the axis of the resulting magnetic field of a certain set of slots will be called the direction specified with an angular position equal to the arithmetic mean of the positions of these slots without taking into account the direction of the flowing current.

Some variants of the electric machine are disclosed in Figs. 3, 4, 5, 6. The magnetic circuit of the stator 1 of the electric machine has a two-pole three-phase winding 2 (the number of pole pairs p = 1), connected in a star. The zero-sequence harmonic injector 3 is connected to the common point of the stator winding star. The electric machine has a salient-pole rotor 4 with slots 5, located with a step of 180/p = 180 mechanical degrees, in which the excitation winding 6 is laid. All slot sides of the multiphase harmonic winding 7 are laid in slots 8, located on the rotor teeth.

Phase A of the harmonic winding corresponds to slots A and -A with angular coordinates of 40° and -20°, counted from the center of a given rotor tooth counterclockwise, respectively. Since each group of slots of the harmonic winding contains one slot and the middle position of the slot groups coincides with the position of the corresponding slots. Therefore, the middles of the slot groups correspond to the slots themselves. The angular distance between the middle directions of the slot groups of the harmonic winding (between the slots) with currents flowing in the opposite direction, located on one tooth, is [40 - (-20)]/p = 60 degrees. The angular distance between the middle directions of the slot groups of the harmonic winding (between the slots) with currents flowing in the opposite direction, located on adjacent teeth, is 180/p = 180 degrees.

On each tooth of the rotor shown in Fig. 4, the two-phase winding of the harmonic exciter is laid in two pairs (groups) of slots with currents flowing in the opposite direction, corresponding to phases A and B. Phase A corresponds to slots (groups of slots) A and -A with angular positions of 40/p = 40° and -20/p = -20°. The axis of the resulting magnetic field of phase A has an angular position of [40 + (-20)]/2 = 10°. Similarly, the axis of the resulting magnetic field of phase B has a position of -10°. The angular distance between the midpoints of the slots of phases A and B is 20°.

As can be seen from Fig. 5, the phases at one end are connected in opposite directions when connected to the rectifier 9, that is, in such a way that when current flows sequentially through phases A and B, the magnetic fields of the phases are mutually weakened.

Fig. 6 shows, without limitation of generality, some examples of the stator winding electric circuit that do not require an inverter. The injector is powered from its own power source or from the stator winding network. Such circuits may have compensating capacitors and a diode bridge connected to the stator winding. The voltage rectified by the diode bridge can power the injector. The compensating capacitors perform a short circuit at the injected frequency if it is 3 or more times higher than the fundamental frequency. Therefore, connecting the injector to the common point of the capacitors included in the star is not necessary. In generator applications, the stator winding can be connected to the load directly or to a global or local power grid. It is also possible to use it as a generator of direct voltage taken from the DC terminals of the diode bridge (passive rectifier).

Fig. 7 shows an example of an electric circuit of a stator winding containing a DC link, a three-phase inverter 10 and an injector 3.

Regardless of the presence of an inverter, the injector may contain passive elements (inductors, transformers, capacitors) to match the connection to the common point of the star and to galvanically isolate the injector from the stator winding at the fundamental frequency and at frequencies below the fundamental frequency.

Fig. 8 shows an example of a rotor of an electric machine, in each group of slots of the harmonic winding of which there are two slots.

Fig. 9 shows the rotor of an electric machine in which one tooth contains three pairs of groups of slots with currents flowing in the opposite direction. Phase A corresponds to slots A and -A. Slot A has an angular position of 50/p = 50°. Slot -A has an angular position of -10/p = -10°. Therefore, the axis of the resulting magnetic field of phase A has an angular position

[50 + (-10)]/2 = 20°. Similarly, the axis of the resulting magnetic field of phase B has an angular position of -20°. Therefore, the axes of the resulting magnetic field of phases A and B are spaced by [20 - (-20)] = 40°. Phases A and B are connected in opposite directions and are connected to the rectifier through a common section C in a matched connection with phases A and B. For example, when current flows sequentially through slots A and C, the magnetic field is amplified. The angular direction of the axis of the resulting magnetic field of phase C is between the axes of the resulting magnetic field of phases A and B.

Fig. 10 shows a rotor of an electric machine in which a two-phase harmonic winding on one tooth contains one group of phase A slots and a pair of groups of phase B slots with currents flowing in the opposite direction. The axes of the resulting magnetic field of phases B and A coincide with the middle of the rotor tooth, and, therefore, coincide with each other.

Fig. 11. Shows options for connecting compensating capacitors to the harmonic winding. Capacitors can be connected between the phase and the common wire, as well as between phases.

Fig. 12 shows it with slots leading to the winding grooves and passing between the teeth.

Fig. 13 illustrates possible ranges of deviation of angular distances between groups of slots and phase axes of a two-phase winding of a harmonic exciter without a common branch. The dash-dotted lines with one dot show the middle directions of groups of slots of one phase. The dash-dotted lines with two dots show the axes of the resulting field of phases A and B.

As a result of using a multiphase winding of a harmonic exciter in the considered variants of the invention, the zero-sequence current of the stator winding at any rotor position creates a magnetic flux in at least one of the phases of the harmonic exciter winding, which increases the efficiency of excitation energy transfer. Therefore, the machine can be started at any rotor position. Increasing the efficiency of excitation transfer allows for a decrease in the field of injected harmonics in the gap, which, together with the fact that excitation energy is transferred continuously, at any rotor position, also reduces torque pulsations and vibrations. In addition, the efficiency of excitation energy transfer allows for an increase in specific characteristics and efficiency even without using a hysteresis current source to power the stator winding. In addition, the angular size of the tooth may differ from 120 el. degrees. For example, it may be greater than this value, which opens up additional opportunities for increasing the efficiency and specific characteristics.

The use of compensating capacitors in the harmonic winding circuit allows to compensate for the reactive component of the current flowing in the injector circuit, which reduces the negative effect of leakage inductance. As a result, the efficiency and specific characteristics increase, including with an increase in the gap. As a result, torque pulsations and vibrations are additionally reduced.

The rectifier on the rotor can be either passive (usually a diode bridge) or active. The advantage of a passive rectifier is its greater simplicity. The use of an active rectifier allows for compensation of the reactive component of the current flowing in the injector circuit without compensating capacitors. In addition, field-effect transistors have very low resistance in the open state. All this, together with the possibility of flexible rectification control, allows for a reduction in torque pulsation and an increase in the efficiency of excitation energy transfer, resulting in increased efficiency and specific characteristics.

The presence of means for measuring current and/or voltage and/or active and/or reactive power of the injected channel allows for excitation control and transfer of excitation energy more efficiently. For example, with compensating capacitors connected to the harmonic winding, it is possible to adjust the frequency at which resonance is achieved, and the reactive power is significantly reduced or compensated. As a result, the efficiency and specific characteristics are increased.

The presence of slots extending to the outer circumference of the rotor (Fig. 12), located between two adjacent teeth, makes it possible to reduce scattering along the q axis, which helps to reduce saturation, reduce losses in the rotor, and increase efficiency and specific characteristics.

Claims (11)

1. An electric machine having a stator magnetic circuit with a 2p-pole three-phase winding connected in a star, a zero-sequence harmonic injector connected to the common point of the stator winding connected in a star, a salient-pole rotor with slots located at a pitch of 180/p degrees, into which the excitation winding is laid, a harmonic exciter winding on the rotor, a rectifier on the rotor connected by DC outputs to the excitation winding and AC terminals to the harmonic exciter winding, characterized in that all slot sides of the harmonic exciter winding are laid in slots located on the rotor teeth, the harmonic exciter winding has two or more phases, the angular distance between the middle directions of the groups of slots of the harmonic exciter winding with currents flowing in the opposite direction, located on one tooth rotor, is (55-65)/p degrees, the angular distance between the middle directions of the groups of slots of the harmonic exciter winding with currents flowing in the opposite direction, located on adjacent rotor teeth, is (170-190)/p degrees. 2. An electric machine according to claim 1, in which the two-phase winding of the harmonic exciter on each tooth of the rotor is laid in two pairs of groups of slots with currents flowing in the opposite direction, corresponding to phases A and B; the axes of the resulting magnetic field of phases A and B are located at a distance of no less than 15/p and no more than 25/p degrees; when connected to the rectifier, phases A and B are connected in opposite directions. 3. An electric machine according to claim 1, in which the multiphase stator winding is connected to an inverter. 4. An electric machine according to item 1, in which the three-phase stator winding is connected to compensating capacitors. 5. An electric machine according to claim 1, wherein the two-phase winding of the harmonic exciter on one tooth is laid in three pairs of groups of slots with currents flowing in the opposite direction; the axes of the resulting magnetic field of phases A and B are located at a distance of no less than 35/p and no more than 45/p degrees; phases A and B are connected in opposite directions and are connected to the rectifier through a common section C in a matched connection with phases A and B; the axis of the resulting magnetic field of phase C is located between the middle directions of the sets of slots of phases A and B. 6. An electric machine according to claim 1, in which the two-phase winding of the harmonic exciter on one tooth is laid in one group of slots of phase A and a pair of groups of slots of phase B with currents flowing in the opposite direction; the axis of the resulting magnetic field of phase B and the mid-direction of the group of slots A are deviated from the middle of the tooth by no more than 5/p degrees. 7. An electric machine according to item 1, in which compensating capacitors are connected to the winding of the harmonic exciter. 8. An electric machine according to item 1, in which a passive rectifier is located on the rotor, connected by direct current outputs to the excitation winding and by alternating current terminals to the winding of the harmonic exciter. 9. An electric machine according to item 1, in which an active rectifier is located on the rotor, connected by direct current outputs to the excitation winding and by alternating current terminals to the winding of the harmonic exciter. 10. An electric machine according to claim 1, in which the injector is equipped with means for measuring the active and/or reactive power of the injected signal. 11. An electric machine according to claim 1, in which the rotor has slots extending to the outer circumference of the rotor or to the slots of the harmonic winding, passing between two adjacent teeth.