RU2164053C1 - Method for regulating ac motor speed of rotation (alternatives) - Google Patents

Abstract

FIELD: special- and general-purpose synchronous, hysteresis, and induction motors. SUBSTANCE: first alternative implies variation of motor supply voltage shaped by means of inverter by applying feedback signal proportional to phase of second derivative of motor phase current within one of ON/OFF intervals of inverter (π/3÷2π/3)+πn or (2π/3÷π)+nπ relative to π/2 value, where n = 0, 1, 2 ... According to second alternative feedback signal is shaped in proportion to phase at zero value of inverter input current second derivative zero within ON/OFF intervals of inverter relative to π/2 value of respective motor phase. Proposed method is also useful for damping oscillations of motor frequency of rotation. EFFECT: improved speed of response to variations in motor frequency of rotation. 7 cl, 7 dwg, 2 ex

Description

 The invention relates to electrical engineering and can be used to stabilize the speed of alternating current electric motors (and in particular damping its oscillations) - synchronous, synchronous-hysteretic or asynchronous, both general and special, made without access to the shaft, for example, gyroscopic, or used in multi-motor synchronous rotation electric drives.

 A known method of stabilizing the rotational speed of AC electric motors, according to which the voltage of the electric motor is changed by the signals of a phase discriminator located in the feedback loop on the position of the rotor, the inputs of which receive two signals: a constant frequency of the setpoint and a variable frequency of the sensor located on the motor shaft [E .L. Tansky. Precision engine speed stabilization systems. - M .: Energy, 1975, p. 1-20].

 The disadvantage of this method is that, with all the obvious positive qualities, it requires a high-precision sensor located on the motor shaft, which is not always feasible in a number of electromechanical devices, in particular, special designs — gyroscopes, ultracentrifuges, electrospindles, etc.

 There is also a method of stabilizing the speed of an asynchronous electric motor, implemented by introducing positive feedback on the absolute sliding of the rotor and affecting the voltage of the motor [A.S. Sarbatov, R.S. Sandler. Automatic frequency control of induction motors. - M .: Energy, 1974, p. 129].

 The disadvantage of this method is the low speed due to the fact that this method assumes the presence on the shaft of an induction motor of an absolute slip sensor. In addition, the calculation of absolute slip by this method involves the measurement of at least several periods of rotation of the motor shaft.

 There is a method of amplitude control that implements stabilization of the rotational speed of a synchronous-hysteresis motor without access to a shaft powered by a voltage inverter [B.A. Delektorsky, V.N. Tarasov. Hysteresis driven drive. - M.: Energoatomizdat, 1983, p. 108]. According to this method, the voltage of the motor is regulated by the signals of a current sensor located in the power supply circuit of the inverter, and controlling the low-frequency component of the current consumption of the inverter.

 The disadvantage of this method is the low speed due to the fact that the selection of the low-frequency component requires a sufficiently long time. Without the use of special additional methods for stabilizing the magnetic state of the rotor material of a synchronous-hysteresis motor, the current in the power supply circuit of the voltage inverter is not an unambiguous function of the position of the rotor. In addition, the circulation of reactive energy in a stand-alone voltage inverter occurs depending on the power factor across various circuits - either with the participation of a compensating capacitor, or inside the inverter itself, thereby introducing additional phase distortions into the measurement process. An additional disadvantage of this method is the difficulty of isolating the low-frequency component at low values of the frequency of oscillation of the rotor, slow changes in the load or magnetic state of the material of the rotor.

 Closest to the proposed method is a method of damping oscillations of three-phase hysteresis motors powered by a static frequency converter, consisting of a three-phase voltage inverter with a rectangular-step shape of the output voltage and voltage regulator, voltage variation in proportion to the first derivative of the active motor power [application of Germany N 2726410, H 02 P 7/44].

 The disadvantage of this method is the lack of speed and accuracy due to the fact that the active power signal obtained as the product of the rectangle-step output voltage of the inverter by a phase current with a substantially non-sinusoidal shape additionally contains information about the power loss in the motor and, strictly speaking, is not adequate power on the shaft of the engines. In addition, the regulation of the motors according to this method requires a preliminary measurement of power for a certain number of periods of the supply voltage and the allocation of the first harmonic component of the active power. In addition, it should be noted that the presence of a large number of sensors in the DC and AC circuits of the inverter and the controller, the signals of which are corrected for the active power signal, complicates the implementation of the method.

 The main task to which the invention is directed is to increase the speed and accuracy of stabilization of the frequency of rotation of AC electric motors - synchronous, synchronous-hysteresis or asynchronous, powered by static frequency converters containing an inverter with a rectangular-step shape of the output voltage.

 The task is achieved in that in the first embodiment of the method of stabilizing the rotation speed of AC motors powered by static frequency converters containing an inverter with a rectangular-step shape of the output voltage, the power supply voltage of the electric motor generated by the inverter is changed by means of a feedback signal.

 What is new is that the feedback signal is generated proportionally to the phase of the second derivative of the phase current of the electric motor at one of the inverter switching intervals (π / 3 ÷ 2π / 3) + nπ or (2π / 3 ÷ π) + nπ relative to the value π / 2, where n = 0, 1, 2, ...

; фаза В; фаза

; фаза C; фаза

и т.д. и сформированный таким образом сигнал обратной связи корректируют в зависимости от параметров конкретного электродвигателя.In addition, the feedback signal is formed in proportion to the phase of the second derivative of the phase currents at the same switching intervals of the phases of the inverter in the sequence: phase A; phase

; phase B; phase

; phase C; phase

etc. and the feedback signal thus formed is corrected depending on the parameters of the particular electric motor.

 The problem is achieved in that in the second variant of the method for stabilizing the rotational speed of AC electric motors powered by static frequency converters containing an inverter with a rectangular-step shape of the output voltage, the power supply voltage of the electric motor generated by the inverter is changed by means of a feedback signal.

 What is new is that the feedback signal is generated proportionally to the phase of the second derivative of the inverter consumption current at the inverter switching intervals with respect to the π / 2 value of the corresponding phase of the electric motor, and the feedback signal obtained in this way is adjusted depending on the parameters of a particular electric motor.

 The combination of technical solutions related to the variants of the method is due to the fact that they solve the same problem - increasing the speed and accuracy of stabilization of the rotational speed of AC electric motors in essentially the same way: by determining the phase of the second derivative of the phase (output) current or current consumption of the (input) inverter at the corresponding switching intervals with respect to the π / 2 value of the corresponding phase of the electric motor.

 The proposed options differ in the composition of the operation of generating a feedback signal, which are nevertheless equivalent in terms of the achieved result, which provides an increase in speed and accuracy of stabilization of the frequency of rotation of AC electric motors. For these reasons, the essence of the inventions for each of the variants of the method is equivalent, and significant differences that ensure the achievement of the task cannot be combined by generalizing or alternative features and therefore are presented in the form of independent objects.

 Due to the indicated combination of distinguishing features, the proposed method variants allow stabilization of the rotational speed of alternating current electric motors using information directly from their phase current or inverter consumption current without using additional high-precision sensors located on the motor. Since the signal used actually carries direct information about the position of the rotor, and is additionally adjusted depending on the parameters of a particular electric motor, the method is highly accurate, and if it is possible to update information on the position of the rotor six times during the supply voltage period (in accordance with the principle of operation of a three-phase bridge inverter ) achieved high performance devices that implement this method.

 In FIG. 1 is a functional diagram of a device that implements the proposed variants of a method for stabilizing the rotational speed of AC electric motors.

 In FIG. Figures 2 and 3 show the phase currents of alternating current electric motors with an ideal open circuit and an active current equal to zero, as well as in the presence of an active phase current (with a load on the shaft or active motor resistances that are not equal to zero).

 FIG. 4 illustrates the determination of an inflection point in a phase current curve whose phase is used as a primary signal for implementing the stabilization method.

 FIG. 5 illustrates the effect of the active resistance of the stator phase winding on the accuracy of the formation of the primary signal for implementing the stabilization method.

 In FIG. 6a, b show the output phase rectangle-step voltage of the inverter and the corresponding consumption current, respectively.

 In FIG. Figure 7 shows the dependence of the error Δθ on the stator resistance and the load angle θ for synchronous (and hysteretic) motors or (with a similar designation) the angle θ of the phase shift of the rotor current relative to the air gap EMF for asynchronous motors (for example, a gyroscopic synchronous-hysteresis motor).

 The device comprises an alternating current electric motor 1 connected by a stator circuit through a phase current sensor 2 to the output of a voltage inverter 3, the power input of which is connected through a consumption current sensor 2 'to the output of a voltage regulator 4, the input of which is intended to be connected to a direct current source. The voltage inverter 3 with its control multiphase input is connected to the first multiphase output of the control circuit 5, the second output of which is connected to the first input of the switch 6 connected to the second input with a phase current sensor 2 or a consumption current sensor 2 '. The output of the switch 6 through a series-connected differentiator 7 and a zero-organ 8 is connected to the first input of the phase discriminator 9, the second input of which is connected to the third output of the control circuit 5 through the reference origin forming device 10. The output of the phase discriminator 9 is connected to the main input of the calculator 11 and the first input of the circuit 12 for determining the switching intervals. The control input of the calculator 11 is connected to the output of the circuit 12 for determining the switching intervals, the second input of which is connected to the fourth output of the control circuit 5. The output of the calculator 11 through the digital-to-analog converter 13 and the comparator 14 is connected to the control input of the voltage regulator 4. Information about the current load angle of synchronous (and hysteresis) motors or sliding of the asynchronous rotor is output directly from the output of block 13.

 As sensors 2, 2 'can be used standard sensors based on the Hall effect. Inverter 3 is performed according to a bridge circuit with a bridge of reverse diodes, voltage regulator 4 - according to a compensation scheme. Switch 6 is a set of logically switched keys. The differentiator 7 and the comparison device 14 are performed on operational amplifiers with resistive-capacitive circuits. Zero organ 8 is a comparator. A set of devices 5, 9 - 12, producing the functions of generating the inverter control signals and converting the feedback signal, can be implemented on a programmable microcontroller. The digital-to-analog converter 13 is made on standard microcircuits.

 A method of stabilizing the rotation speed is as follows. The formation of electromagnetic forces and torques in electric machines of alternating current can be considered as a result of the interaction of the stator current spatial waves that are motionless relative to each other and the distribution waves of the magnetic field induction along the circumference of the rotor. Moreover, a non-zero torque is created by the interaction of these waves of the same order, and harmonics of different orders create moments whose total value is zero [A.I. Voldek. Electric cars. - L .: Energy, 1974, p. 515].

 In induction motors, the formation of a current sheet, induction of the rotor and torque is a consequence of the slip of the rotor relative to the spatial waves of the stator MDS.

 In synchronous-hysteretic motors, the current layer is physically absent, the rotor induction spatial wave is formed due to the orientation of the magnetic domains of the rotor material according to the stator MDS, and the moment is a result of the mutual spatial arrangement ("load angle") of these waves and does not depend on the constant degree of rotor excitation slip.

 In synchronous electric motors of both magnetoelectric and electromagnetic design, the rotor induction spatial wave is a quantity independent of the stator MDS, and the moment, other things being equal, is a consequence of the mutual spatial arrangement of the stator MDS waves and the rotor induction wave, which is rigidly coupled in contrast to the synchronous hysteresis motor with a rotor in any operating mode.

 In the presence of temporary and spatial harmonic components of electromagnetic fields in the air gap of all the above electric motors, the shape of the spatial component does not depend on the shape of the supply voltage, but is determined only by the design features and the distribution of the stator phase windings in space. In practice, they strive to organize the sinusoidal law of the spatial MDS of the stator, which in asynchronous and synchronous hysteresis motors leads to a sinusoidal waveform of induction of the rotor, and of high quality in special-purpose electric machines - gyromotors, ultracentrifuges, electric spindles, etc.

 Sinusoidally distributed rotating spatial waves of the induction of the rotor create a sinusoidal reaction in the form of an emf of rotation in the fixed stator windings. This reaction is most easily observed in the phase current of an alternating current electric motor, powered by a static frequency converter with a rectangular-step shape of the output voltage. In this case, the static converter is not only a motor power source, but also a kind of master of the standard step action, which allows to distinguish the presence of the spatial sinusoidal component of the current wave from the rotor against the background of an exponentially time-varying component of the current from the inverter.

где R₁, X_экв - соответственно активное сопротивление фазной обмотки статора и эквивалентное реактивное сопротивление фазы двигателя;
k = R₁/X_экв;
α = arctg (X_экв/R₁);
E_r - фактическая ЭДС ротора;

круговая частота;
φ - текущее значение фазы;
U_d - постоянное напряжение на входе инвертора.When powering an AC electric motor from a three-phase voltage inverter with the simplest rectangular-step voltage form, the phase current I ₁ at switching intervals 0 ÷ π / 3; π / 3 ÷ 2π / 3; 2π / 3 ÷ π for the operating point when neglecting losses in the magnetizing circuit of the equivalent circuit can be represented by the currents I ₁ (φ), I ₂ (φ), I ₃ (φ), respectively:

where R ₁ , X _equiv - respectively, the active resistance of the stator phase winding and the equivalent reactance of the motor phase;
k = R ₁ / X _equiv ;
α = arctan ( _Xeq / R ₁ );
E _r is the actual EMF of the rotor;

circular frequency;
φ is the current phase value;
U _d - constant voltage at the input of the inverter.

In this case, the physical and quantitative content of X _equiv and _Er is determined for a particular type of AC motor.

 In FIG. 2a is a graphical explanation of the phase current shape using an example of a synchronous-hysteresis motor with perfect idle and active resistance of the stator winding tending to zero.

In FIG. 2b - d - also at various degrees of magnetization of the rotor. The symmetric shape of the current with respect to π is characteristic, regardless of the degree of magnetization of the rotor. This form is explained by the fact that the purely reactive component of the inverter current I _μ , which is always symmetric with respect to π and consists practically of line segments, is summed in this case with the current component from the actual EMF E _r I _2Er , also symmetrical with respect to π, since the load angle θ = 0 . In the presence of active resistance of the stator winding R ₁ (as well as losses in steel r _m , increasing load on the shaft or in slip mode), the symmetry is broken. In this case, the current increases in the interval 0 ÷ π, and to the greatest extent in the zone φ = 0 ÷ π / 2 due to an increase in the active component (Fig. 3a, b). Obviously, a similar pattern is observed for synchronous motors. For asynchronous motors at idle, the actual rotor EMF (in contrast to the given one) is E _r ≈ 0, the phase current is almost the exponential segments (or direct at R ₁ = 0), and only a very small “hysteretic” component is present in the current of the real motor moment. The shape of the phase current of an asynchronous electric motor when loaded and powered by an inverter is similar to the current shape of synchronous machines.

Примечательно то, что и при наличии активного сопротивления обмотки статора (по крайней мере, в диапазонах реальных значений) точка перегиба соответствует углу θ. При обозначении составляющих выражения (2) для тока I₂(φ) соответственно M(R₁,φ) и N(R₁,φ) можно показать, что

Фиг. 5 иллюстрирует выражение (6) для реальных гироскопических синхронно-гистерезисных электродвигателей.Plots of phase currents π / 3 ÷ 2π / 3 and 2π / 3 ÷ π (Fig. 4) are of interest as carriers of information on the load angle θ of synchronous and synchronous-hysteresis machines or (with a similar designation) the angle θ of the phase shift of the rotor current relative to the EMF air gap asynchronous. According to the stated concepts and from FIG. 2a it follows that the inflection point φ _per current curve in the interval π / 3 ÷ 2π / 3 coincides with the only inflection point of the sinusoidal current l _2Er when crossing through zero, which is behind the EMF E _r by π / 2 (the current from the inverter in this interval represents inclined line at R ₁ = 0). If the coordinate φ = π / 2 in the adopted system corresponds to the axis of the phase winding, or, up to a voltage drop across the stator resistance R _1, to the voltage vector U ₁ , then the angle θ = φ _lane -π / 2. At angles θ> π / 6, the inflection point moves to the interval 2π / 3 ÷ π, although the real angles θ of the electric motors used, as a rule, do not exceed the indicated value. It can be mathematically shown that the second derivative of the phase current at the indicated intervals exactly vanishes at the corresponding angles θ and neglecting the stator resistance, i.e. R ₁ _ → 0:

It is noteworthy that in the presence of active resistance of the stator winding (at least in the ranges of real values), the inflection point corresponds to the angle θ. When designating the components of expression (2) for the current I ₂ (φ), respectively, M (R ₁ , φ) and N (R ₁ , φ), we can show that

FIG. 5 illustrates expression (6) for real gyroscopic synchronous-hysteresis motors.

 The calculated and experimental data show that the error in determining the load angle of synchronous (and hysteresis) motors and the phase shift angle of the rotor current relative to the EMF of the air gap of asynchronous motors at the inflection point in the phase current curve (i.e., by the fact that the second derivative with respect to the current angle) is exerted not by the value of the active resistance of the stator winding, but by a slight deviation from zero of the second derivative of the exponential component of the current from the inverter at the measurement point. Indeed, a change in the stator resistance in an equal degree (and in one direction) affects the shift of the current components from the inverter and the actual rotor EMF. However, with increasing stator resistance, starting from zero, the shape of the inverter component of the phase current in the switching interval changes, respectively, from a straight line to an increasingly pronounced exponent. Accordingly, the second derivative of the inverter component changes from zero to a certain value. Given that the second derivative at the inflection point of the sinusoidal dependence always vanishes, an error from the exponential component of the inverter current will appear at the phase current measurement point. So, for the tested synchronous-hysteresis electric motors, the error in determining the load angle in the range of load variation and stator resistance according to the presented method did not exceed 0.04 rad (Fig. 7).

Переходя к приращениям и разлагая выражения (7), (8) в ряд Тейлора в окрестностях точки измерения, после преобразования получим соответствующие выражения для корректировки измеренных значений в форме:

где φ₀ - фаза второй производной фазного тока относительно значения π/2;
θ - истинный угол нагрузки синхронных (и гистерезисных) электродвигателей и угол фазового сдвига тока ротора относительно ЭДС воздушного зазора асинхронных электродвигателей;

где K_U = U_d/E_r,
Известно, что огибающая тока потребления инвертора напряжения складывается из участков фазных токов на интервале π/3÷2π/3 (фиг. 6а) [B.C. Руденко, В. И. Сенько, И.М. Чиженко. Преобразовательная техника. - Киев. Вища школа, 1978, стр. 320]. Исходя из этого факта информацию о точке перегиба на кривых фазных токов на указанных интервалах при углах θ<π/6 можно получить в цепи постоянного тока инвертора.The measurement results can be adjusted, knowing the deviation of the fixed zero value of the second derivative of the phase current from the true value of the determined angle. The correction function is obtained from the condition that the second derivatives of the phase currents vanish on the switching intervals π / 3 ÷ 2π / 3 and 2π3 ÷ π, respectively:

Passing to increments and expanding expressions (7), (8) in a Taylor series in the vicinity of the measurement point, after the conversion, we obtain the corresponding expressions for adjusting the measured values in the form:

where φ ₀ is the phase of the second derivative of the phase current relative to the value of π / 2;
θ is the true load angle of synchronous (and hysteresis) motors and the phase angle of the rotor current relative to the EMF of the air gap of asynchronous motors;

where K _U = U _d / E _r ,
It is known that the envelope of the current consumption of the voltage inverter consists of sections of phase currents in the interval π / 3 ÷ 2π / 3 (Fig. 6a) [BC Rudenko, V. I. Senko, I. M. Chizhenko. Conversion technology. - Kiev. Vishka School, 1978, p. 320]. Based on this fact, information on the inflection point on the phase current curves at the indicated intervals at angles θ <π / 6 can be obtained in the DC circuit of the inverter.

 The device shown in FIG. 1, works as follows.

; фаза B; фаза

; фаза С; фаза

и т.д., где знак <-> над буквой означает инверсию. Нуль-орган 8 определяет фазу φ_0dt второй производной, которая поступает на первый вход фазового дискриминатора 9. При этом на его втором входе присутствует значение фазы π/2. В пусковом режиме на выходе фазового дискриминатора 9 образуется максимальный сигнал, который вводит регулятор 4 напряжения в режим максимального ограничения и таким образом происходит форсированный запуск электродвигателя 1. При достижении электродвигателем 1 рабочей частоты вращения блоки 2, 2', 6-13 начинают постоянное поинтервальное (в зоне коммутации инвертора 60^o (эл.)) отслеживание отклонения угла θ по сигналу второй производной фазных токов.When the supply voltage is applied, the control circuit 5 generates a three-phase voltage system with a relative phase shift of 120 ^o (el.), Necessary for the inverter 3 to operate, as a result of which a three-phase rectangular-step voltage is generated at its output (Fig. 6b). At the time of starting the electric motor 1, the load angle of synchronous (and hysteresis) machines or the phase angle of the rotor current relative to the EMF of the air gap of asynchronous machines is maximum. Differentiator 7 at one of the switching intervals calculates the current value of the second derivative of the inverter phase current with respect to the angle φ = ω ₁ t, information about which comes from the output of switch 6. Depending on the operating mode, which reflects the variants of the presented method, the signal to the input of differentiator 7 through the switch 6 can come either from the sensor 2 'of phase currents, or from the sensor 2 of the consumption current located in the DC circuit of the inverter 3. Obviously, the information from the sensor 2' of the current consumption can be updated six times after power supply riode. In the first case, the signal can be generated either from one of the phases on one of the inverter switching intervals (π / 3 ÷ 2π / 3) + nπ or (2π / 3 ÷ π) + nπ relative to the value π / 2, where n = 0, 1 , 2, ..., or from three phases as the next measuring interval appears, and this also occurs six times during the supply voltage period in the sequence: phase A; phase

; phase B; phase

; phase C; phase

etc., where the <-> sign above the letter means inversion. The zero-organ 8 determines the phase φ _{0dt of the} second derivative, which enters the first input of the phase discriminator 9. At the same time, the value of the phase π / 2 is present at its second input. In the starting mode, the maximum signal is generated at the output of the phase discriminator 9, which enters the voltage regulator 4 into the maximum limit mode, and thus the forced start of the electric motor 1 occurs. When the electric motor 1 reaches the operating speed, the blocks 2, 2 ', 6-13 begin a constant interval ( in the switching zone of the inverter 60 ^o (el.)) tracking the deviation of the angle θ by the signal of the second derivative of phase currents.

где r₂, x_σ2 - соответственно активное сопротивление и индуктивное сопротивление рассеяния фазы ротора.For synchronous (and hysteresis) motors with additional signal correction by the calculator 11 in accordance with expressions (9), (10) this means stabilization of the rotor speed. For the purpose of stabilizing the slip S of induction motors, expressions (9) and (10), calculator 11 implements in the form:

where r ₂ , x _σ2 - respectively, the active resistance and inductive resistance of the scattering phase of the rotor.

When the electric motor is operating, the circuit 12 for determining the switching intervals, realizing the membership function [φ ∈π / 3 ... 2π / 3; φ ∈2π / 3 ... π], leads in the calculator 11 the components A _i , B _i and the rotor parameters of the induction motors included in expressions (9) - (12) in accordance with the working measurement interval. These components are introduced into the calculator 11 and are a function of the parameters of a particular motor, as well as their dependencies on destabilizing factors, and in particular, on the operating temperature t ^o . At the output of the calculator 11 in digital form, there is actually a corrected (true) value of expressions (9), (10) for the angle θ for synchronous (and hysteresis) machines, or for expressions (11), (12), the slip value S for asynchronous through the digital-to-analog Converter 13 enter in the form of a mathematical module on the comparator 14 and after comparing with a given value of the angle or slip to control the voltage regulator 4. The formation of the module of the output values of the calculator 11 is necessary to maintain the sign (type) of feedback in cases where the motors are in the generator mode, for example, in transients.

The proposed method of stabilization of the rotational speed under constant operating conditions and engine parameters in a closed-loop automatic control system operating on a deviation, which is the device for implementing this method, in principle
It is also realized without adjustment according to expressions (9) - (12). However, the introduction of the correction of the measured value of the angle θ not only increases the accuracy of the electric drives when changing the operating modes and parameters of their electric motors, but also allows you to get the exact value of the load angle of synchronous (or hysteresis) motors, as well as the phase angle of the rotor current relative to the EMF of the air gap or slip asynchronous electric motors in measurement modes.

 The device also allows the correct introduction of additional feedback necessary for the implementation of frequency control [A. S. Sarbatov, R.S. Sandler. Automatic frequency control of induction motors. - M .: Energy, 1974].

 Example 1. With an increase in the angle θ of the synchronous (or hysteresis) motor, which can occur due to an increase in the load on the shaft, or stator resistance, or a decrease in rotor excitation, the signal at the output of the comparator 14 also increases, which leads to an increase in the output voltage of the controller 4, inverter 3, the voltage of the motor 1, increase the slope of the angular characteristics of the motor and return the angle θ to its original position.

 Example 2. With an increase in the load on the shaft of an induction motor (with constant rotor parameters), in accordance with the mechanical characteristic, the rotor slip increases, which, all other things being equal, leads, according to (9) - (12), to increase the angle θ. Analogously to example 1, in the end, the voltage on the electric motor increases, which leads to a transition to another mechanical characteristic with the return of a given slip. In fact, in this example, control is sufficient only along the angle θ. In the case of an additional change in the parameters of the rotor (for example, its active resistance), a complete correction according to expressions (11), (12) and slip control are required.

 Thus, the proposed method options allow stabilization of the rotational speed of AC electric motors using information directly from their phase current without the use of additional high-precision sensors located on the electric motor. Since the signal used actually carries direct information about the position of the rotor, the method has high accuracy, and when updating information about the position of the rotor six times during the period of the supply voltage, high performance of devices implementing this method is achieved. In addition, the proposed method automatically assumes the constant availability of current information about the load angles of synchronous and synchronous hysteresis machines, the angles of the phase shift of the rotor current relative to the EMF of the air gap or slip of asynchronous machines. In other words, devices capable of implementing this method are actually non-contact meters of the indicated values and can be used in inverter electric drives using, for example, the principles of vector control.

Claims (7)

 1. The method of stabilizing the rotational speed of AC motors powered by static frequency converters containing an inverter with a rectangular-step shape of the output voltage, in accordance with which the power supply voltage of the electric motor generated by the inverter is changed by means of a feedback signal, characterized in that the feedback signal form in proportion to the phase of the second derivative of the phase current of the electric motor on one of the inverter switching intervals (π / 3 ÷ 2π / 3) + nπ or (2 / 3 ÷ π) + nπ relative value π / 2, where n = 0, 1, 2, .... 2. The method according to claim 1, characterized in that the feedback signal is formed proportionally to the phase of the second derivative of the phase currents at the same switching intervals of the inverter in the sequence: phase A; phase

; phase B; phase

; phase C; phase

etc. 3. The method according to any one of claims 1 and 2, characterized in that for synchronous and synchronous hysteresis motors, the feedback signal is adjusted depending on the parameters of the electric motor in accordance with the expressions:

for the interval (π / 3 ÷ 2π / 3) + nπ,

for the interval (2π / 3 ÷ π) + nπ,
where θ is the load angle;
φ ₀ is the phase of the second derivative of the phase current;
And ₁ , B ₁ , A ₂ , B ₂ - the function of the parameters of a particular motor, determined in accordance with the expressions:

where K _U = U _d / E _r ; U _d - constant voltage at the input of the inverter;
E _r is the actual EMF of the rotor;
k = R ₁ / X _equiv ;
α = arctan ( _Xeq / R ₁ );

R ₁ , X _equiv - respectively, the active resistance of the phase stator winding and the equivalent reactance of the motor phase. 4. The method according to any one of claims 1 and 2, characterized in that for asynchronous electric motors the feedback signal is adjusted depending on the parameters of the electric motor in accordance with the expressions:

for the interval (π / 3 ÷ 2π / 3) + nπ,

for the interval (2π / 3 ÷ π) + nπ,
where S is the slip of the rotor;
r ₂ , x _σ2 - respectively, the active resistance and inductive resistance of the scattering phase of the rotor;
φ ₀ is the phase of the second derivative of the phase current;
And ₁ , B ₁ , A ₂ , B ₂ - the functions of the parameters of a particular motor, determined in accordance with the expressions:

where K _U = U _d / E _r ; U _d - constant voltage at the input of the inverter;
E _r is the actual EMF of the rotor;
k = R ₁ / X _equiv ;
α = arctan ( _Xeq / R ₁ );

R ₁ , X _equiv - respectively, the active resistance of the stator phase winding and the equivalent reactance of the motor phase.  5. A method of stabilizing the rotational speed of alternating current electric motors powered by static frequency converters containing an inverter with a rectangular-shaped output voltage shape, in accordance with which the supply voltage of the electric motor generated by the inverter is changed by means of a feedback signal, characterized in that the feedback signal form in proportion to the phase of the second derivative of the inverter consumption current at the switching intervals of the inverter relative to the value of π / 2 s responsible phase motor. 6. The method according to p. 5, characterized in that for synchronous and synchronous hysteresis motors, the feedback signal is adjusted depending on the parameters of the motor in accordance with the expressions;

for the interval (π / 3 ÷ 2π / 3) + nπ,

for the interval (2π / 3 ÷ π) + nπ,
where θ is the load angle;
φ ₀ - phase of the zero value of the second derivative of the phase current;
And ₁ , B ₁ , A ₂ , B ₂ - the functions of the parameters of a particular electric motor, determined in accordance with the expressions:

where K _U = U _d / E _r ; U _d - constant voltage at the input of the inverter;
E _r is the actual EMF of the rotor;
k = R ₁ / X _equiv ;
α = arctan ( _Xeq / R ₁ );

R ₁ , X _equiv - respectively, the active resistance of the phase stator winding and the equivalent reactance of the motor phase. 7. The method according to claim 5, characterized in that for asynchronous electric motors the feedback signal is adjusted depending on the parameters of the electric motor in accordance with the expressions:

for the interval (π / 3 ÷ 2π / 3) + nπ,

for the interval (2π / 3 ÷ π) + nπ,
where S is the slip of the rotor;
r ₂ , x _σ2 - respectively, the active resistance and inductive resistance of the scattering phase of the rotor;
And ₁ , B ₁ , A ₂ , B ₂ - the functions of the parameters of a particular electric motor, determined in accordance with the expressions:

where K _U = U _d / E _r ; U _d - constant voltage at the input of the inverter;
E _r is the actual EMF of the rotor;
k = R ₁ / X _equiv ;
α = arctan ( _Xeq / R ₁ );

R ₁ , X _equiv - respectively, the active resistance of the phase stator winding and the equivalent reactance of the motor phase.

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