RU2317632C1 - System for vector control of speed of asynchronous electric motor - Google Patents

Abstract

FIELD: systems for automatic control of alternating current electric motors, possible use for frequency control of asynchronous motor speeds.

SUBSTANCE: device features three-phased motor model in natural coordinates of stator and rotor and load moment compensation contour. The system contains magnetic linkage contour and speed contour with slave contours of longitudinal and transverse components of stator current. Informational part of the system includes a device for transforming magnetic linkage of rotor into system of rotating coordinates (x,y) and device for transforming currents from three-phased (a,b,c) system into rotary system of coordinates (x,y), connected to outputs of the model. For forced orientation of machine flow, a contour for automatic tuning of magnetic linkage frequency is used.

EFFECT: ensured qualitative characteristics of systems for vector control of alternating current electric motors with a minimum of check connection sensors.

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Description

The invention relates to the field of automatic control systems for AC electric drives and can be used for frequency regulation of the speed of an induction motor.

A known frequency-current system for controlling the speed of an asynchronous electric motor [1], comprising a speed loop whose error signal is proportional to the active component of the current (load moment) is supplied together with the signal for setting the magnetizing component of the current proportional to flux linkage through the coordinate converter from a rotating reference system to a fixed coordinate system stator to the inputs of the phase currents of an induction motor.

Coordinates are converted using two modulators, an engine angle sensor, a differential angle sensor and a tachometric tracking system.

The disadvantage of this system is the low static and dynamic properties of the control system. This is due to a simplified approach to the implementation of control loops and the lack of feedback on flux linkage. When the moment is formed, the flux linkage may deviate from the set one as a result of changes in the rotor resistance and saturation of the machine. In addition, the influence of cross-connections and the emf of rotation in the phase current circuits is not taken into account, which leads to amplitude and phase errors in the formation of phase currents. Optimization of transients in the phase current circuits is difficult, since the regulators must have a variable transmission frequency.

A well-known vector control system for the speed of an asynchronous electric drive with a rotor flux model of the motor rotor (see Fig. 11 [3]), containing two control channels for the frequency converter implemented on the basis of the mains voltage rectifier and autonomous voltage inverter, one power output of which is direct and the other two through current sensors are connected to the windings of an induction motor. The first channel is four-circuit and contains a position controller, a speed controller with a limiting unit, a torque controller, a transverse component of the stator current in a rotating coordinate system. The second channel is dual-circuit and contains the flux linkage regulator and the longitudinal component of the stator current in series in a rotating coordinate system. The outputs of the current regulators of two channels through a current converter from a rotating coordinate system (x, y) to a fixed coordinate system (α, β) and a converter of a two-phase coordinate system (α, β) to a three-phase system (a, b, c) are connected to the inputs -pulse modulator connected by outputs with control inputs of keys of an autonomous inverter. The first input of the position controller is connected to the position controller, and the second to the output of the integration unit, connected by the input together with the second inputs of the speed controller and the flow coupler to the output of the speed sensor of the induction motor.

The outputs of the current sensors are connected through a converter of a three-phase current system (a, b, c) to a two-phase (α, β) to a current converter from a system of fixed (α, β) coordinates to a rotating coordinate system (x, y), one of the output signals of which I _sx defining a longitudinal component of the stator current is connected to the second input of the current regulator for component I _sx, and through aperiodic link with the first inputs of the division unit, with which a signal is generated proportional to the slip frequency ω _r of the rotor, and multiplying by which the odds iruetsya signal proportional to the dynamic motor torque, the other signal is proportional to a transverse component of the stator current I _sy connected to the second current controller inputs of component I _sy, dividing and multiplying unit. The output of the aperiodic link with which the signal I _mrx proportional to flux linkage is generated is connected as a feedback signal to the second input of the flux linkage controller and to the control input of the restriction unit, the multiplier output is connected to the second input of the torque regulator, the output signal ω _{r of the} divider is through an adder and a block integration is connected to the deploying inputs of the coordinate transformers, the second input of the adder is connected to the output of the speed sensor. The synchronous frequency is defined as the sum of the signal ω _r from the output of the divider and the signal ω from the output of the speed sensor and is fed through the integration unit to the blocks of trigonometric converters

The disadvantage of this system is the low adjusting properties caused by the fact that the behavior of the model in the system of rotating coordinates is not consistent with the real processes taking place in the engine. This is due to the fact that the mathematical model is defined with a number of assumptions, which include: the sinusoidality of voltages and currents in the motor, the derivation of the model equations under the assumption that the frequencies of the stator and rotor circuits of the motor are constant and there is no influence of cross-links in the rotor circuits, i.e. for stationary operation and lack of transient modes. In addition, the use of current sensors in a significant range of output frequencies of the converter leads to measurement errors and a decrease in accuracy. The introduction of a torque control loop reduces the speed of the control system, and its effectiveness is significantly reduced with inaccurate determination of flux linkage.

The closest in technical essence and in the totality of the principles of implementation to the claimed invention is a vector control system for the speed of an asynchronous electric rotor AD [3], selected as a prototype.

A vector control system for the speed of an asynchronous electric drive contains a flux linkage circuit that includes a series-connected comparison element connected to a rotor and feedback flux link reference signal and a flux linkage controller, a speed loop that includes a serially connected element to compare a rotor rotation frequency reference signal and a feedback from a sensor speed and a dual-circuit parametric speed controller with a limiting unit, the second input of which is additionally connected inen with an output by a speed sensor, the outputs of the flux linkage and speed controllers are connected to the corresponding subordinate current loops, each of which contains a series-connected adder of the signal for setting the current and feedback from the corresponding output of the current transformer from the system (α, β) to the rotating coordinate system (x, s) and a current regulator, the outputs of each of which are connected through a unit for compensating the emf of rotation and cross-connections, the coordinate converter from the rotating system (x, y) to the stationary system (α, β) and a converter of a two-phase signal system into a three-phase to the control inputs of a frequency converter connected by power outputs through current sensors to the windings of an asynchronous electric motor, in the gap of which two sensors of the main flux linkage components are installed on the Hall elements, the outputs of which are through a rotor flux linkage calculator in a fixed coordinate system (α, β) are connected to the inputs of the flux linkage converter from a fixed coordinate system (α, β) to a rotating coordinate system (x, y), the outputs of the phase current sensors are connected through a converter of the three-phase current system to two-phase to the second information inputs of the calculator of the rotor flux linkage components in the fixed coordinate system (α, β) and the inputs of the current converter from the fixed coordinate system (α, β) to the rotating coordinate system (x, y ), the rotation angle of which relative to the fixed coordinate system (α, β) is φ _c = ∫ω _c t, the second expanding inputs of the coordinate transformers are connected to the outputs of the guides sinφ _c and cosφ _{c of the} two-phase generator, sec the third and third inputs of the compensation unit for the emf of rotation and cross-connections to the outputs of the current transformer from the fixed coordinate system (α, β) to the rotating coordinate system (x, y) and to the output of the speed sensor, in addition, the system contains a loop for automatically adjusting the frequency of the flux linkage connected frequency controller and the division unit, the output of which sets the synchronous frequency ω _s with connected to the input of the two-phase generator and the fourth input of the compensation unit of the emf of rotation and cross-connections, and the control input with together with the third control input of the parametric speed controller, the feedback input of the rotor flux link circuit comparison element and the fifth input of the rotational emf and cross-coupling compensation unit, is connected to the output Ψ _{rx of} the flux link converter from the fixed coordinate system (α, β) to the rotating coordinate system (x, s) through the first low-pass filter, and the frequency controller input is connected to the output Ψ _{ry of the} rotor flux linkage converter from a fixed coordinate system (α, β) to a rotating system mu coordinates (x, y) through the second low-pass filter.

The disadvantage of this system is that its implementation requires the completion of common industrial blood pressure by installing Hall sensors in the engine clearance to control the components of the flux linkage. This narrows the scope of systems with direct measurement of the flux linkage vector.

The essence of the invention is to solve the problem of stabilizing the control system without the use of current sensors and flux linkage. This is achieved by introducing a full three-phase model of an induction motor in the natural coordinates of the stator and rotor, as well as additional auto-tuning loops.

The technical result consists in providing quality indicators of vector control systems for AC electric drives with a minimum of feedback sensors.

The specified technical result in the implementation of the invention is achieved by the fact that in the known system of vector control of the speed of an asynchronous electric drive containing a flux link, including a series-connected element for comparing the task of flux linkage and feedback and a flow regulator, a speed loop that includes a series-connected element for signal comparison setting the rotor speed and feedback from the speed sensor, parametric speed controller with unit m limitation, the second input of which is additionally connected to the output of the speed sensor, the outputs of the flow coupler and speed controllers are connected to the corresponding slave current loops, each of which contains a series-connected adder of the current signal and feedback from the corresponding output of the current converter from the three-phase system (a, b , c) into a rotating coordinate system (x, y), current controllers, the outputs of which are connected through a unit for compensating the emf of rotation and cross-connections, a converter from a coordinate system (x, y) into a three-phase system (a, b, c) and a pulse-width modulator to an autonomous inverter control unit connected by power inputs to a power source and outputs with asynchronous motor windings, the third and fourth inputs of the emf compensation unit rotation and cross-connections are connected to the outputs of the current transformer from a three-phase system (a, b, c) into a rotating coordinate system (x, y), as well as sequentially connected synchronous frequency controller, division unit and integrator, the output of which is connected n with the expanding inputs of the current converter, coordinate converter from the rotating system (x, y) to the three-phase system (a, b, c), the peculiarity is that a motor model is introduced in the natural coordinates of the stator and rotor, the three outputs of which are proportional to the phase currents the stator is connected to the inputs of the current transformer from the system (a, b, c) into a rotating coordinate system (x, y), the rotor flux linkage converter to the rotating coordinate system (x, y), the three inputs of which are connected to three other outputs of the model in proportion поток _rx - to the feedback input of the element for comparing the flux linkage, Ψ _ry output - to the input of the synchronous frequency controller, the third adder, two inputs of which are connected to the integrator output and the seventh output corresponding to the coordinate of the rotor angle of the model, and the output is connected to the deploying input of the rotor flux linkage converter to the rotating coordinate system (x, y), the eighth model output corresponding to the coordinate of the rotation frequency is connected together with the speed sensor output growth to the third element of comparison, the output of which through the load moment compensation regulator is connected to the input of the coordinate of the model's static moment.

The analysis of the prior art by the applicant, including a search by patent and scientific and technical sources of information, and the identification of sources containing information about analogues of the claimed invention, allowed to establish that the applicant did not find an analogue characterized by features identical to all the essential features of the claimed invention. The definition from the list of identified analogues of the prototype, as the closest in the set of essential features of the analogue, allowed to identify the set of essential distinguishing features in relation to the applicant's technical result in the claimed device set forth in the claims.

Therefore, the claimed invention meets the condition of "Novelty."

To verify the compliance of the claimed invention with the condition "Inventive step", the applicant conducted an additional search for known solutions in order to identify signs that match the distinctive features of the claimed device from the prototype. The search results showed that the claimed invention does not follow explicitly from the prior art, since the effect of the transformations provided for by the essential features of the claimed invention on the achievement of the technical result, in particular, the claimed invention does not provide for the following:

1) using the rotor model of the motor in the coordinate system rotating with synchronous frequency;

2) the use of three-phase coordinate converters and a pulse-width modulator is not included in the differing part of the claims, since the principle of their implementation is known;

3) the use of a crucial unit for the formation of the components of the flux linkage of the rotor.

The described invention is not based on a change in quantitative features, the introduction of known blocks and the presentation of such features in conjunction follows from the main idea of the invention - the use of autonomous model properties to realize the ability to configure the drive without introducing feedback sensors and connecting the motor. In the analogues of the claimed invention, these blocks are used for another functional purpose and have other functional relationships.

Therefore, the claimed invention meets the condition of "Inventive step".

The invention is illustrated by graphic materials which depict: in Fig. 1 is a functional diagram of a vector control system for the speed of an induction motor, in Fig. 2 is a structural diagram of a three-phase model of the motor in the natural coordinates of the stator and rotor. The inventive "Vector control system for the speed of an asynchronous electric drive" contains a flux link, which includes a series-connected element 1 comparing the rotor flux link signal and the feedback component по _rx flux link, flux link controller 2, a speed loop that contains the element 3 comparing the signal for setting the rotor speed and feedback from the output of the speed sensor, parametric speed controller 4 with b eye of limitations. The outputs of the flux linkage controller 2 and the speed loop controller 4 are connected respectively through adders 5, 6 of the slave current loops, current regulators 7, 8, two channels of the rotational emf and cross-link compensation block 9, and a converter 10 from the rotary coordinate system (x, y) to three-phase system (a, b, c) to the pulse-width modulator 11 of the control unit of the autonomous inverter 12, the power inputs of which are connected to a constant voltage source, and the outputs to the windings of the induction motor 13, as well as to the motor model 14 governmental systems stator and rotor coordinates. Three model outputs proportional to the stator phase currents, through a 15 current converter from a three-phase system (a, b, c) to a rotating coordinate system (x, y), are connected to the corresponding second inputs of adders 5, 6 of the current circuits as feedback signals and to the first two inputs of the compensation unit 9. Three other model outputs proportional to the flux linkage of the rotor phases are connected to the rotor flux linkage converter 16 to a rotating coordinate system (x, y), one of the outputs of which characterizing the Ψ _rx rotor flux linkage component is connected to the feedback input of the flux link circuit comparison element 2, s 3rd input of the compensation emf 9 and cross connections and the control input of the speed regulator 4 Ψ _ry second output transducer 16 via the controller 17 the synchronous frequency dividing unit 18, and integration unit 19 in F s connected to the inputs of the trigonometric transducers of the engine model 14 and coordinate transformers 10, 15. The output of the integrator 19 and the model output characterizing the coordinate of the rotor rotation angle are connected to the third adder 20, whose output equal to the phase difference is connected to the deployment input of the converter 16. The model output corresponding to the coordinate ω of the rotor speed, through the third comparison element 21 and the load torque compensation controller 22 is connected to its input corresponding to the coordinate of the static moment. The feedback inputs of the elements 3, 4, 21 are connected to the output of the engine speed sensor 23. The control inputs of the controller 4 and the division unit 18 are connected to the output Ψ _{rx of} the flux linkage converter of the rotor 17.

The principle of organization of the regulatory system is based on the organization of operating conditions under which the formation of moment and flux linkage was carried out independently of each other. These conditions are satisfied when the components Ψ _rx and Ψ _ry of the rotor flux linkage vector are controlled in the coordinate system rotating at a synchronous speed and when working with the rotor flux link components Ψ _rx = const and Ψ _ry = 0. The block diagram of an induction motor, in this case, is similar to the block diagram of a DC motor and contains two main circuits: stabilization of the rotor flux linkage and speed control. The torque control is carried out only due to one value of I _{sy the} transverse component of the stator current.

- переходная индуктивность статорной обмотки, L_s, L_r, L_m - индуктивности статорной и роторной цепи и их взаимная индуктивность. Для компенсации влияния внутренних перекрестных связей на статор со стороны ротора формируются корректирующие сигналы ωK_rΨ_rx, К_rΨ_rx/Т_r, которые вводятся на выходе регуляторов тока. Здесь K_r=L_m/L_r - коэффициент связи ротора, Т_r - постоянная времени ротора, ω - частота вращения ротора. Учитывая, что переходная индуктивность L′_S, составляющие потокосцепление ω_СL′I_sy, ω_СL′I_sx не оказывают значительного влияния на переходные процессы. Влиянием связи ωK_rΨ_ry с учетом реализации условия Ψ_ry=0 можно пренебречь. Действие составляющей ωK_rψ_rx в силу значительной инертности ротора также не оказывает существееного влияния на переходные процессы системы с обратными связями.The control system (see figure 1) is implemented in accordance with the principles of constructing systems of subordinate control of parameters. The rotor flux linkage control channel Ψ _rx contains a subordinate circuit of the current component I _sx , and the current component circuit I _{sy is} subordinate to the velocity circuit. The parameters of the regulators 2, 4, 7 and 8 are selected based on the conditions for setting the circuits to a modular optimum. Dual-speed speed controller. The first circuit contains an integrator with a controlled input for the mismatch of the second. The second circuit includes an additional element of comparison, a proportional link, a divider and a restriction block. The transfer functions of the regulators in this case correspond to PI regulators. To isolate the control circuits and eliminate the influence of cross-connections between the stator flux linkage components, at the output of the current regulators, using block 9, compensating signals ω _c L ' _s I _sy , ω _c L' _s I _{sx are formed} , where ω _c is the synchronous frequency,

- transient inductance of the stator winding, L _s , L _r , L _m - inductors of the stator and rotor circuits and their mutual inductance. To compensate for the effect of internal cross-linking on the stator from the rotor side, correction signals ωK _r Ψ _rx , K _r Ψ _rx / Т _{r are formed} , which are introduced at the output of the current regulators. Here K _r = L _m / L _r is the rotor coupling coefficient, T _r is the rotor time constant, ω is the rotor speed. Given that the transient inductance L ′ _S constituting the flux linkage ω _С L′I _sy , ω _С L′I _sx do not significantly affect the transients. The influence of the coupling ωK _r Ψ _ry , taking into account the realization of the condition Ψ _ry = 0, can be neglected. The action of the component ωK _r ψ _rx , due to the significant inertia of the rotor, also does not exert an existing effect on the transients of the feedback system.

To control the components of the stator current and rotor flux linkage, a motor model is used.

The initial system of matrix equations for the stator and rotor voltages of the three-phase HELL recorded in natural coordinate systems has the form:

Where

R _s , R _r - resistance of the stator and rotor windings; I _sa , I _sb , I _sc - stator phase currents; I _ra , I _rb , I _rc - rotor phase currents; Ψ _sa , Ψ _sb , Ψ _sc , Ψ _ra , Ψ _rb , Ψ _rc are the flux linkages of the phases of the stator and rotor, respectively.

Maximum mutual inductance of stator and rotor windings

.

.

When the rotor is rotated through an angle φ relative to the stator, the expressions for flux linkage are:

where for a symmetric three-phase machine

Here L _s , L _r - respectively, the inductance of the stator and rotor windings.

The motor moment for the natural coordinates of the motor is defined as the partial derivative of the electromagnetic energy stored in the stator and rotor windings in angle

,

,

which gives the following expression

where φ is the angle of rotation of the rotor relative to the stator.

Drive Motion Equation

where J is the moment of inertia of the drive, M _c is the moment of load on the motor shaft.

The structural diagram of the model of the engine 14 in accordance with equations (1) ÷ (6) is presented in figure 2. As the main input coordinates of the model, the voltage on the stator windings is used. This allows the simplest pairing of the model with real values acting on the control object, for example, using voltage dividers connected to a star.

The relationship between the phase quantities and the components of the stator current vector in the directions of the x and y axes is determined from the equation

Where

This equation determines the correspondence between the instantaneous values of the phase quantities and the components of the generalized vector.

The transition from the phase quantities of the model in the fixed coordinate system to the orthogonal components of the stator current in the rotating coordinate system is carried out by the Converter 15 in accordance with the following expressions:

The control signals of the pulse-width modulator 19 of the autonomous inverter are generated by the converter 10 by switching from the orthogonal components of the generalized vector to a three-phase voltage system in accordance with the following equations:

U _sa = U _sx cosφ _c -U _sy sinφ _s ;

U _sb = U _sx cos (φ _c -2π / 3) -U _sy sin (φ-2π / 3);

U _sc = U _sx cos (φ _c + 2π / 3) -U _sy sin (φ + 2π / 3).

The equations of transition from the phase values of the rotor flux linkage to the flux linkage components in the rotating coordinate system, which are implemented using the transducer 16, have the form:

;

;

.

.

The synchronous frequency ω _{c is} monitored by monitoring the flux linkage component Ψ _ry using the synchronous frequency controller 17 and the division unit 18. An integrator 19 is used to form the sweep phase φ _c = ∫ω _c dt 19. Phase mismatch (φ _с -φ) between the stator and the rotor is determined using the adder 20.

To avoid mismatch between the model and the engine when the load torque on the motor shaft changes, a load torque compensation loop is used. The mismatch in the speed of the model and the engine (ω and ω _∂ ) is generated by the adder 21 and through the controller 22 is supplied to the input of the model corresponding to the coordinate of the static moment M _c . Given the fact that the transfer coefficient of the integrator of the model, which is identically equal to the moment of inertia of the engine, a fixed value - optimization of processes in the circuit is achieved by controller 22, the transfer function of which corresponds to the real differentiating link. This circuit also compensates for other possible speed deviations caused by the non-identical engine and model parameters, as well as their change during operation.

Initial adjustment of the control system is possible without the use of an engine speed sensor. To do this, it is enough to close the velocity loop in the output coordinate ω of the model.

Thus, the above information indicates the following conditions are met when using the claimed system:

- the essential features characterizing the essence of the invention, in principle, can be repeatedly used in the technique of automatic control of variable frequency drives in various industries with obtaining a technical result, which consists in regulating transient conditions and ensuring stability conditions without using current sensors and flux linkage;

- to implement the principle of building a system, both analog and analog-to-digital controls can be used, while signal microprocessors and microcontrollers have an advantage;

- means embodying the claimed invention in its implementation, regardless of their type, can ensure the achievement of the technical result perceived by the applicant.

Therefore, the claimed invention meets the condition of "Industrial applicability".

Information sources

1. Brodsky V.N., Ivanov B.C. Drives with frequency-current control. M .: Energy, 1974, p. 37-47, p. 134-138, Fig. 3-2.

2. Kochetkov V.D. et al. Control systems for AC electric drives with microprocessor control / V.D. Kochetkov, L.X. Datskovsky, A.V. Biryukov, Yu.M. Gusyatsky, V.G. Rogova // Elektrotehn. industry. Ser. 08. Electric drive: Review, inform. - 1989. Issue 26. - S.1-80.

3. RF patent for the invention No. 2158055, class. Н02Р 21/00, 2000.

Claims (1)

A vector control system for the speed of an asynchronous electric drive, comprising a flux linkage circuit, including a serially connected element for comparing the flux linkage and feedback and a flux linkage regulator, a speed loop, which includes a serially connected element for comparing the signal for setting the rotor speed and feedback from the speed sensor, parametric speed controller with limiting unit, outputs of flow control and speed controllers are connected via appropriate slave current loops, each of which contains a series-connected adder of the current command and feedback signal from the corresponding output of the current converter from the three-phase system (a, b, c) to the rotating coordinate system (x, y), current regulators, two channels of the EMF compensation unit rotation and cross-connections, a coordinate converter from a rotating system (x, y) to a three-phase system (a, b, c) and a pulse-width modulator to an autonomous inverter control unit connected by power inputs to a power source, and you odes - with windings of an asynchronous electric motor, the first and second inputs of the compensation unit for rotation EMF and cross-connections are connected to the outputs of the current transformer from the three-phase system (a, b, c) into a rotating coordinate system (x, y), as well as the synchronous frequency controller connected in series , a division unit and an integrator, the output of which is connected to the deploying inputs of the current transformer from the three-phase system (a, b, c) to the rotating coordinate system (x, y), the coordinate transformer from the rotating system (x, y) to the three-phase system (a, b, c), the feedback input of the parametric speed controller is connected to the output of the speed sensor, characterized in that a three-phase motor model is introduced in the natural coordinates of the stator and rotor, the three inputs of which are connected to the power outputs of the autonomous inverter, and the first three outputs proportional to the stator phase currents, connected to the inputs of the current transformer from the three-phase system (a, b, c) to the rotating coordinate system (x, y), the rotor flux linkage converter to the rotating coordinate system (x, y), three inputs to which are connected to three other outputs of the model proportional to the flux linkages of the rotor windings, the output ψ _rx is to the feedback input of the element for comparing the flux link, the third input of the compensation module for rotation emf and cross-connections and the control inputs of the parametric speed controller and division block, the output ψ _ry is _connected to the input of the synchronous frequency controller, the third adder, two inputs of which are connected to the integrator output and the seventh model output, corresponding to the coordinate of the rotor rotation angle, and the output is connected to to the input of the rotor flux linkage converter to the system of rotating coordinates (x, y), the third comparison element, the two inputs of which are connected respectively to the eighth output of the model corresponding to the speed coordinate and the output of the speed sensor, and the output through the load torque compensation controller is connected to the coordinate input static moment of the model.

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