RU2254666C1 - Alternating-current drive - Google Patents

Abstract

FIELD: electrical engineering; variable-speed ac drives.

SUBSTANCE: newly introduced in proposed electric drive is adaptive torque regulator that generates rotor flux linkage vector by shaping phase-by-phase assignment of its instant values whose frequency and amplitude depend on torque assignment. Angle of 45 deg. between stator current and rotor flux linkage vectors optimal from the standpoint of minimizing stator input current is attained by frequency variation. Rotor flux linkage is maintained by introducing phase modifiers whose outputs are connected to control inputs of pulse-width modulation current regulator. Inverter functions to produce stator phase currents at frequency and amplitude required to produce desired torque on condition that stator input current coming from supply mains is minimized and magnetic circuit is used as much as possible. Electric drive operates in real three-phase coordinate system which enables complete elimination of various coordinate conversions complicating calculations and needing mode rigorous requirements to management controller.

EFFECT: enhanced power and dynamic characteristics.

1 cl, 2 dwg

Description

The invention relates to electrical engineering, in particular to variable AC drives, and can be used to minimize energy losses when feeding an asynchronous electric motor from a frequency converter, as well as controlling the torque and speed of asynchronous electric motors.

Known AC electric drive containing an induction motor connected by stator windings to the outputs of a pulse current transducer made with control inputs for the frequency and for the orthogonal components of the stator current, a speed sensor mounted on the shaft of the induction motor, connected in series to the speed reference unit, a comparison element and proportional-integral speed controller, while the other input of the comparison element is connected to the output of the speed sensor [1].

The disadvantage of this device is the difficulty of regulating the controlled coordinates of the current vectors and flow due to the presence of multiple coordinate transformations, requiring significant computing power for calculating trigonometric functions.

The closest to the invention in technical essence and the achieved result is an AC electric drive containing a three-phase inverter, the power outputs of which are connected via phase current sensors to two stator windings of an asynchronous electric motor, and the control inputs of the inverter through a control pulse generation unit and connected to pulsed phase current sensors the current regulator is connected to the outputs of the direct transducer of two-phase-three-phase coordinates, the inputs of which are connected to the outputs of the direct about the Cartesian coordinate converter, while the orthophase and common-mode outputs of the direct Cartesian coordinate converter are connected to the outputs of the orthophase current controller and the common-mode current controller, respectively, the input of the orthophase current controller is connected to the output of the adaptive torque controller, the input of which torque is connected to the output of the speed controller, which sets the input connected to the speed reference unit [2].

The disadvantages of this technical solution are the complexity of the control controller due to the presence of a large number of computational operations associated with coordinate transformations that require determination of instantaneous values of trigonometric functions in each operation cycle.

The proposed AC drive contains a three-phase inverter, two power outputs of which are connected through the phase current sensors to two stator windings of the induction motor, and the control outputs of the inverter are connected to the output of the pulse forming unit, a speed sensor mounted on the shaft of the asynchronous motor, the output of which is connected to the negative input comparison unit, the positive input of which is connected to the speed reference unit, and the output of the comparison unit is connected to the input of the proportional-integral p speed regulator, the third power output of the inverter is directly connected to the third winding of the motor stator, the output of the speed regulator is connected to the input of the torque regulator, the output of which is connected to the first input of the unit for setting the instantaneous values of the rotor flux linkage, which has three phase outputs, each of which is connected to a positive input one of the three phase comparison blocks, the negative inputs of which are connected to the phase blocks for calculating the rotor phase flow, and the outputs of the three phase flow comparison blocks with the inputs of the rotor phase flow controllers of the motor, the outputs of which are supplied to the first three inputs of the PWM current controller block, the six outputs of which are connected to the six control inputs of the three-phase inverter, the outputs of two current sensors are connected to the input of the current adder, and also connected to two inputs of the PWM block a current regulator, and also connected to the inputs of two phase blocks for calculating the rotor phase flow of the motor, the output of the current adder is connected to the input of the third phase block for calculating the rotor phase flow and the input of the PWM current regulator, the outputs of the rotor phase flow calculation blocks are connected to the negative inputs of the three phase rotor flow comparison blocks, the output of the proportional-integral speed controller is connected to the first input of the angle tangent setting unit, the output of the torque regulator is connected to the second input of the angle tangent setting unit, the output of which is connected to the first input a unit for generating a rotor magnetic flux frequency, the second input of which is connected to an output of a speed sensor, an output of a unit for generating a magnetic flux rotor speed and connected to the second input of the unit for setting the instantaneous values of the rotor flux linkage, and also connected to the first input of the slip calculation unit, the output of the speed sensor is connected to the second input of the slip calculation unit, the output of which is connected to the input of the calculation unit of the integration time constant, the output of which is connected to three blocks of rotor phase flow controllers, and three phase blocks of rotor flow calculation.

In this AC drive, the set value of the electromagnetic moment is provided at the minimum values of the stator current, which is achieved by maintaining a constant angle between the stator current vectors and rotor flux linkage of 45 °.

In figure 1. a functional diagram of an AC electric drive is given; figure 2. - the dependence of the stator current on the angle between the stator current vectors and the rotor flux at a constant electromagnetic moment.

The AC drive contains a three-phase inverter 1, two power outputs of which are connected through current sensors 2 and 3 to two stator windings of an induction motor 4, and a third power output of inverter 1 is connected directly to the third stator winding of motor 4. A speed sensor 5 is installed on the shaft of the motor 4. The control inputs of the inverter 1 are connected to the outputs of the pulse width modulation (PWM) block of the current regulator 6. The outputs of the current sensors 2, 3 are connected to the inputs of the current adder 7. The outputs of the current sensors 2, 3 along with the output the current adder 7 is supplied to the PWM block of the current controller 6. The output of the speed sensor 5 is connected to the negative input of the speed comparison unit 8, the positive input of which is connected to the speed setting unit 9. The output of the speed comparison unit 8 is connected to the proportional-integral input nth speed controller 10. The output of the speed controller 10 is connected to the input of the torque controller 11. The output of the proportional-integral speed controller 10 is connected to the first input of the angle tangent setting unit 12, the second input of which is connected to the output of the torque controller 11. The output of block 12 is connected to the first input the unit for generating the frequency of rotation of the magnetic flux of the rotor 13, the second input of which is connected to the output of the speed sensor 5. The output of the torque regulator 11 is connected to the first input of the unit for generating the task of instantaneous flow values the heating of the rotor 14, the second input of which is connected to the block 13. Three phase outputs of the block 14 are connected to the positive inputs of one of the three phase comparison blocks 15, 16, 17, the negative inputs of these blocks are connected to the outputs of the phase blocks of the calculation of the rotor phase flow 18, 19, 20. The outputs of the three phase flow comparison blocks 15, 16, 17 are connected to the inputs of the phase flow controllers of the rotor 21, 22, 23, the outputs of which are fed to the first three inputs of the PWM block of the current regulator 6, the six outputs of which are connected to the six control inputs of the three-phase inverter 1 . IN the outputs of the current sensors 2, 3 are connected to the inputs of two phase blocks for calculating the flow of the phase of the rotor 18, 20. The output of the current adder 7 is connected to the input of the phase block for calculating the flow of the rotor 19. The outputs of the current sensors 2, 3, as well as the output of the current adder 7 are connected to three the PWM inputs of the current regulator 6. The output of the speed sensor 5 is connected to the first input of the slip calculation unit 24, the second input of which is connected to the output of the magnetic flow rate generating unit of the rotor 13. The output of the slip calculation unit 24 is connected to the input of the time constant calculation unit and integration 25, the output of which is connected to three blocks of rotor phase flow controllers (21, 22, 23), and three phase blocks of rotor flow calculation (18, 19, 20).

Electric AC operates as follows.

The inverter 1 feeds the stator windings of the induction motor 4 through pulse-width modulated power voltage pulses through the sensors 2, 3 of the phase currents, the duration of which is determined by the control pulses coming from the output of the PWM current regulator 6. The formation of the task on the PWM block of the current regulator 6 is as follows. The speed reference signal ω ^* ₂ from the speed reference block 9 is compared with the signal of the current rotor speed ω ₂ from the speed sensor 5. The difference thus formed is fed to the input of the proportional-integral speed controller 10, at the output of which the task is generated at the electromagnetic moment.

The task for the moment is supplied to the torque regulator 11. The unit operates in two stages. At the first stage, the module of the rotor flux linkage vector is calculated based on the task at the moment and the condition that the angle between the stator current vectors and the rotor flux linkage should be equal to 45 °, according to the formula

where L _r is the inductance of the rotor, p _n is the number of pairs of poles of the induction motor. The choice of the angle of 45 ° was carried out from the condition of minimizing the stator current consumption by a vector electric drive when forming the moment according to the formula

where L _m is the mutual inductance of the phases, φ _r is the angle between the stator current vector and the rotor flux linkage.

At the second stage of operation of the torque regulator, the module of the given flux linkage calculated at the previous stage is limited to a maximum equal to the value of the saturation of the motor magnetic circuit ψ _{r max} .

Thus, in the further operation of the vector control system, saturation is not taken into account.

The moment reference from the speed controller 10, as well as the reference to the rotor flux linkage module from the torque controller, are the input values of the angle tangent reference block 12, according to the formulas

This block is necessary to ensure a given value of the electromagnetic moment in the case of limitation of the rotor flux linkage module to the maximum. In this case, the required angle will be more than optimal.

The unit for generating the rotational speed of the magnetic flux of the rotor 13, depending on the current rotor speed ω ₂ and setting the supported angle between the stator current vectors and the rotor flux link, generates at the output a target for the rotational flux vector of the rotor, at which the required angle is formed in the asynchronous electric drive between the driving vectors of the moment. The formula is as follows

where T ₀ is the time constant calculated from sliding, equal to:

where R ' ₂ - reduced to the stator resistance of the rotor, s - slip calculated by the formula

The sign in equation (4) corresponds to the sign of the task of the moment M ^* . The frequency ω ₁ thus formed, along with the task of the rotor flux linkage module, is fed to the input of the instant rotor flux linkage formation unit 14 that implements the formula:

c рассчитанными в блоках обратной связи по потоку ротора 18, 19, 20. Представленный электропривод работает в естественной системе координат, что избавляет от необходимости применять двухфазно-трехфазный преобразователь координат. Мгновенные фазные значения потокосцепления вычисляются в блоках 9, 10, 11 из реальных значений тока по передаточной функции Лапласа, каждая из которых имеет передаточную функцию:The tasks thus formed for phase rotor flux linkages are supplied to the inputs of the comparison blocks 15, 16, 17, respectively. On these blocks, the set instantaneous values of the rotor flux linkage are compared

c calculated in the feedback blocks on the flow of the rotor 18, 19, 20. The presented drive operates in a natural coordinate system, which eliminates the need to use a two-phase-three-phase coordinate converter. The instantaneous phase values of flux linkage are calculated in blocks 9, 10, 11 of the real current values by the Laplace transfer function, each of which has a transfer function:

where ψ _r (p), I _s (p) is the operator image of the flux linkage of the rotor and the stator phase current, p is the Laplace operator, L _m is the mutual inductance of the AD phase.

The instantaneous value of the rotor flux is not directly proportional to the current, but varies according to an aperiodic law, the time constant of which is a slip function (5), calculated in block 24. The flux linkage regulators 21, 22, 23 have a transfer function:

которые наряду с действительными значениями (I_sa, I_sb, I_sc) поступают на вход импульсного регулятора тока. Сигнал мгновенного фазного тока I_sb рассчитывается на сумматоре 7 через мгновенные фазные значения токов (I_sa, I_sc), поступающих с датчиков тока 2, 3.where T _f is the Butterworth filter time constant, taken equal to the inverse proportion to the frequency of the PWM comparison operations of the current regulator 6. At the output of the rotor flow controllers, tasks for instantaneous stator phase currents are generated

which, along with the actual values (I _sa , I _sb , I _sc ) are fed to the input of the pulse current regulator. The signal of the instantaneous phase current I _{sb is} calculated on the adder 7 through the instantaneous phase values of the currents (I _sa , I _sc ) coming from the current sensors 2, 3.

In figure 2. The dependence of the stator current on the angle between the stator current and rotor flux vectors, shown in relative units, is shown. The dependence graph shows how the angle between the stator current vectors in the natural characteristic changes with increasing load on the shaft of the induction motor and a change in the stator current required for its formation. As the graph shows, at rated load, the stator current is reduced by 9%, in relation to the drive working directly from the network.

The advantage of the proposed AC electric drive is:

- in working with a real three-phase coordinate system, which eliminates the numerous transformations;

- taking into account the dynamics of changes in the phase values of the rotor flux depending on the change in the phase values of the stator current, which increases the accuracy and speed of the ongoing processes.

Bibliography

1. USSR patent No. 544820, cl. Н 02 Р 5/40 "Electric drive with asynchronous machine" Felix Blaschke. Priority 08/10/1970. Publ. 02/25/77. Bull. Number 7.

2. RF patent No. 1515322, cl. Н 02 Р 7/42 "Electric drive of alternating current" Mishchenko V.A. Priority 05/11/1984. Publ. 10/15/89. Bull. No. 38.

Claims (1)

An AC electric drive containing a three-phase inverter, two power outputs of which are connected through the phase current sensors to two stator windings of the induction motor, and the control inputs of the inverter are connected to the outputs of the PWM current regulator unit, a speed sensor mounted on the shaft of the asynchronous motor, the output of which is connected to the negative input of the comparison unit, the positive input of which is connected to the speed reference unit, and the output of the comparison unit is connected to the input of the proportional-integral speed controller characterized in that the third power output of the inverter is directly connected to the third winding of the stator of the motor, the output of the proportional-integral speed controller is connected to the input of the torque regulator, the output of which is connected to the first input of the unit for generating the instantaneous values of the rotor flux linkage having three phase outputs, each of which is connected to the positive input of one of the three phase rotor flow comparison blocks, the negative inputs of which are connected to the phase blocks of the rotor phase flow calculation, and the outputs of the three phase rotor flow comparison blocks are connected to the inputs of the motor rotor phase flow controllers, the outputs of which go to the first three inputs of the PWM current regulator block, the six outputs of which are connected to the six control inputs of the three-phase inverter, the outputs of two phase current sensors are connected to the input of the current adder as well as connected to two inputs of the PWM current controller block, and also connected to the inputs of two phase blocks for calculating the flow of the phase of the motor rotor, the output of the current adder is connected to the input of the third phase of the rotor phase flow calculation unit and the input of the PWM current controller, the output of the proportional-integral speed controller is connected to the first input of the angle tangent setting unit, the output of the torque controller is connected to the second input of the angle tangent setting unit, the output of which is connected to the first input of the rotation frequency generating unit the rotor magnetic flux, the second input of which is connected to the output of the speed sensor, the output of the rotor magnetic frequency generating unit is connected to the second input of the task forming unit instantaneous values of the rotor flux linkage, and is also connected to the first input of the slip calculation unit, the output of the speed sensor is connected to the second input of the slip calculation unit, the output of which is connected to the input of the calculation unit of the integration time constant, the output of which is connected to three blocks of rotor phase flow controllers and three phase rotor flow calculation units.

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