SU1757041A1 - Ac electric drive - Google Patents

Abstract

Usage: in machine tools, industrial robots. Essence: in an electric drive, a rotational frequency sensor 8 is made on a shaper of 9 pulses, integrators 10 and 13, a pulse width determiner 11 and a threshold element 12. Feedback in frequency of rotation is formed in a closed loop tracking the value of the input period the signal to the sensor 8 rotational speed 7 Il.

Description

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figure 1

The invention relates to electrical engineering, in particular to electric drives of alternating current, built on the basis of synchronous motors, and can be used in electric drives of machine tools, industrial robots, etc., where reliability, accuracy and smoothness of regulation are required.

An alternating-current electric drive is known, comprising a synchronous electric motor, on the shaft of which a sine-cosine-rotating

transformer, the input winding of which is connected to the output of the reference frequency generator, frequency converter, outputs connected to the phase terminals of the root winding of a synchronous

motor, one control input with the output of the first control unit, second control input with the output of the speed controller, the inputs of which are connected to the outputs of the setpoint and the frequency sensor.

The reference frequency generator has a second output, and the sine-cosine rotating transformer has a second input winding connected to the second output of the said generator, the output winding of the specified rotating transformer is connected to the inputs of the first control unit and the rotation frequency sensor.

In the known electric drive, the rotational speed is provided with two additional outputs and is designed as a serially connected module allocation unit, a comparator, a single vibrator and a sign change node, the second input of which is connected via a differentiating node to the module allocation module input, and a two-channel rotation frequency controller is made in the form of two multiplication blocks, to the first inputs of which the comparators are connected.

The disadvantages of the known valve motor drive are low stability and noise immunity due to the presence of differentiation and multiplication units.

Also known is a valve motor containing a synchronous motor and power amplifier with a control circuit (converter), as well as a rotational speed sensor consisting of a switch, a switch control unit, a reference voltage source of the scale factor block, and a rotation frequency signal generating unit. Three inputs of the speed sensor are connected to two outputs of phase-sensitive rectifiers of the control circuit and outputs of the preamplifier.

The switch reproduces the value of the angle of rotation of the rotor shaft against time, made from separate sections of the approximated curves of the output voltages of phase-sensitive rectifiers. The rotational frequency signal generating unit is a model of a valve

electric motor, adjusted by the difference of the current value of the angle (obtained from the output of the switch) and its evaluation obtained in the model. The output of the rotational speed sensor based on a sine-cosine and rotating transformer in a known electric drive is an estimate in this model.

A disadvantage of the known device is its removable complexity, complexity in

configuration and, as a consequence, low reliability. In addition, since there are discontinuities in the output voltage curve of the switch (the dependence of the voltage proportional to the angle versus time)

exclusion of short-term dips in the rotational speed estimation curve, as an output signal of the rotational speed sensor is not used directly, the estimate obtained in the valve model

the motor and the output of the sample-hold unit. When the motor shaft is in the zone of discontinuity of the function and from the angle in time, the output of the speed sensor is the last value of the speed estimate (when entering the specified zone). Thus, in the specified interval, the actual frequency of rotation of the engine shaft is not controlled. This disadvantage limits the range of speed control in a known electric drive.

The closest in technical essence to the present invention is an AC electric drive containing

synchronous electric motor, on the shaft of which a sine-cosine rotary transformer is installed, the input winding of which is connected to the output of the reference frequency generator, frequency converter, outputs connected to the phase terminals of the core of the synchronous electric motor, one control input with the output of the first control unit, the second control the input of the output of the speed regulator, the inputs of which are connected to the outputs of the setpoint and the rotational speed sensor, the last of which is provided with a driver m pulses to one input

and two exits which entrance forms

input of the rotational speed sensor, and a reset integrator, the control input of which is connected to one output of the pulse former.

In the known electric drive, the feedback signal on the rotation frequency is formed by the electronic circuit of the rotation speed sensor by processing information from the output of the rotor position sensor. The circuit contains an adder, two multipliers; two zero order clamps and two reset integrators controlled by a pulse driver connected to a reference frequency generator included in the converter.

The multiple conversion of the signal and the complexity of the circuit due to the presence of analog multipliers determine low reliability, limit the range of rotational speed control and are a drawback of the circuit.

The purpose of the invention is to increase the reliability and extend the range of speed control, as well as simplify and improve the accuracy of the electric drive.

The AC drive contains a synchronous motor, on the shaft of which there is a sine-cosine rotating transformer, the input winding of which is connected to the output of the reference frequency generator, a frequency converter, outputs connected to the phase terminals of the synchronous motor crust, one control input with the output of the first the control unit, the second control input, with the output of the rotational speed regulator, whose inputs are connected to the outputs of the sensor and the rotational speed sensor, the last one of which is provided with a pulse generator with one input and two outputs, the input of which forms the input rotation speed sensor, and an integrator with reset, a control input coupled to one output of the pulse shaper. New in the proposed AC drive is that the reference frequency generator is provided with a second output, and the sine-cosine rotating transformer is a second input winding connected to the second output of said generator, the output winding of the specified rotating transformer is connected to the inputs of the first control unit and a rotational speed sensor, which is additionally equipped with a three-port pulse width terminator, the first and second inputs connected to

the pulse generator outputs, the threshold element and the second integrator, the output of which forms the output of the rotational speed sensor and connected between the output of the specified determinator and the integrator input with a reset, equipped with a second input for supplying a bias voltage, output connected to the input of the threshold element, the output of which is under 0 keys to the third input of the pulse width determiner.

FIG. 1 shows the block diagram of the proposed AC drive; in fig. 2 is a block diagram of a pulse body; in fig. 3 is a block diagram of a pulse determiner; in fig. 4-6 - drive elements; in fig. 7 are oscillograms of voltage signals at points in the drive circuit.

0 The electric drive contains a synchronous motor 1, on the shaft of which a sine-cosine rotary transformer 2 is installed, the input winding of which is connected to the output of the generator 3 of the reference frequency, the frequency converter 4, the outputs connected to the phase terminals of the core winding of the synchronous motor 1 by one control input - with the output of the first control unit 5, the second control input — with the output of the rotation speed controller 6, the inputs of which are connected to the outputs of the setpoint 7 and the rotational speed sensor 8, It is equipped with a pulse shaper 9 with one input and two outputs, the input of which forms the input of the rotational speed sensor 8, and an integrator with a reset 10, the control input of which is connected to one output of the pulse shaper 9.

0 The reference frequency generator 3 is provided with a second output, and the sine-cosine rotating transformer 2 is equipped with a second input winding connected to the second output of the reference frequency generator 3. The high-voltage winding of the sine-cosine rotating transformer 2 is connected to the inputs of the first control unit 5 and the rotational speed sensor 8, which is additionally equipped with a three-input

0 by the determinant 11 of the pulse duration, the first and second inputs connected to the outputs of the imaging unit 9 pulses, the threshold element 12 and the second integrator 13, the output of which forms the output

5 of the rotational speed sensor 8 and connected between the output of the three-input pulse width determiner 11 and the integrator input with reset 10 equipped with a second input for supplying a bias voltage, an output connected to the input

the threshold element 12, the output of which is connected to the third input of the three-input pulse width determiner 11,

FIG. 2 is a block diagram of a pulse driver 9 consisting of a sequence of connected

null comparator 14, one-shot 15, inverter 16, one-shot 17 and inverter 18. Shaper 9 also contains a delay element 19, the input of which is connected to the Y output of the one-shot 15, and the output to the input of element 2И-НЕ 20, the output of which is connected to the second input the second one-shot 17. The outputs of the inverter 18 and the element 20 are respectively the first and second outputs of the driver 9.

FIG. 3 shows a block diagram of a pulse determiner 11 comprising inverters 21-23, elements ZI 24 and 25, RS trigger 26 and an operational amplifier 27 with bias resistors 28 and input 29. The first input of the determiner 11 is connected via inverter 21 to the first inputs of elements 24 and 25. The second and third inputs of the determiner 11 are connected respectively with the inputs of inverters 22 and 23 and with the second inputs of elements 25 and 24, respectively. The outputs of inverters 22 and 23 are connected respectively with the third inputs of elements 24 and 25, the outputs of which are connected respectively to R and S-inputs trig Gera 26 The trigger output 26 is connected to the input resistor 29 of the amplifier 27.

FIG. 4 shows an example of the implementation of the one-shot 15 (17); FIG. 5 - integrator 18, in FIG. B - integrator with reset 10.

The drive works as follows.

When a voltage frequency reference voltage is input to the drive input, a voltage appears at the converter output, the synchronous motor 1 rotates and rotates the sensor 2. The input windings of the sensor 2 are powered from a two-phase generator 3 of the reference frequency (O0. On the output winding of the sensor 2 is formed sinusoidal voltage

U2 A sin (wot (-y (t)) (1)

where (f () is the current value of the rotation angle of the rotor of the sensor, the sign of which depends on the direction of rotation.

The expression (1) can be represented as

U2 A sin ((Do g 2P (Wep) t (2)

where 2P is the number of pole pairs of sensor 2;

(l) vr engine speed 1

Voltage U2 is fed to the input of the converter, where it is used to form the supply voltage of the synchronous motor 2, and to the input of the driver 9. To illustrate the operation of a series of drive assemblies in FIG. 7 shows waveforms. From the sinusoidal voltage LJ2 (Fig. 7a), the null comparator 14 forms rectangular oscillations (Fig. 75) with the same

period. The falling edge (transition from + to -) of these oscillations triggers a one-shot 15, the output of which forms a sequence of pulses of duration m 1 (Fig. 7c). These pulses, after inversion by inverter 16 (Fig. 7d), trigger a one-shot 17, forming a sequence of pulses of duration t 2 (Fig. 7e). These pulses after inversion by inverter 18

arrive at the first output element 20 (Fig. 7e). At the output of element 20, a pulse of duration t z n + ha + lt (Fig. 7g) is formed, where A r is the delay of the one-shot 17 at start-up. Delay element

19 pulls the leading edge of the pulse (Fig. 7c) by the indicated value Dg to eliminate the dips in the pulse (Fig. 7g) (shown by dotted lines).

The integrator's first input with reset 10 (Fig. 6) receives the output voltage of the integrator 13 11d4v, the second input has a bias voltage UCM, and the control input receives pulses from the first output of the former 9. At the output of the integrator 10, a sawtooth voltage is formed (Fig 7h), the slope of which is proportional to the algebraic sum of the stresses UCM + Ufl4e, and the duration is determined by the period of the pulse e,

including switch key capacitor integrator 10.

At the output of the threshold element 12, a sequence of pulses (Fig. 7i) appears, the duration of which at a given (fixed) voltage value of the threshold of Unop 12 element depends on the algebraic sum of UCM + D4v, and at a constant value of UCM depends only on D4V. The determinator 11 compares the duration of the pulses M and I as follows:

The pulse e through the inverter 21 blocks (zeroes) the elements AND 24 and 25, at the inputs of the trigger 26 O and the trigger does not change the state in the pulse existence interval e. This ensures synchronization of the compared pulses - the origin of the G pulse

TA Ti -tz where Ti is the period of the output signal of the DPR,

Since Ti tz more than 100 times, we can assume that

G 4 Tl ftfe + ftV

The duration of the pause of the pulse And is inversely proportional to the specified algebraic sum

G59 GID ± ID4V

The determinator 11 compares the intervals g 4 and g s and outputs a relay signal, the polarity of which depends on which of the intervals is greater.

Comparison of the durations of the periods of these sequences (And and F) produces the determiner 11 as follows (Fig. 7).

A pulse of duration r2, formed by the one-shot 17 in the driver Q, provides reset of the integrator 10 and zero commands to the R and S inputs of the trigger 26 (the zero point is zero initial conditions). The trigger 21 is in one of the states (0 or 1) determined by the comparison result in the previous clock cycle.

Suppose, at output 26 1 (Fig. 7k, the beginning of the diagram after pulse e), at the output of the inverter 27 - (minus U - negative voltage). The integrator 13 begins to integrate the positive increment of the output voltage. The total voltage (1) d4v + Osm) at the input of the integrator 10 increases, which will lead to an increase in the inclination of the saw at the output 10 (Fig. 7h). This will lead to the fact that the pulse (unit level) in the sequence And is worse than in the sequence G. At the input of the ZI element 24 there are three units, at the output 1, the trigger 26 switches to the zero state. The occurrence of 1 in the G sequence after the AND sequence no longer changes the state of the trigger 26, i.e. logical O from the output of the inverter 23 blocks the ZI element 25 until the appearance of a pulse e. The appearance of the pulse e zerphus both ZI elements 24 and 25 and a new beat begins. The work of the determinator 11 is similar for the appearance of 1 in the sequence F earlier than in the sequence I.

Thus, if an impulse (high level) in the sequence F comes earlier, the trigger 26 is thrown (or remains) into a single state and

the output of the determinator 11 (the output of the operational amplifier 27) is negative voltage. If earlier a pulse arrives in the sequence I, then the output of the determinator 11 is a positive voltage.

A change in the speed of rotation of the engine shaft will lead to a change in the period T1. Tracking period duration t1. the circuit will change the voltage Ud4v in the appropriate direction by an appropriate amount in order to ensure that the values of T1 and T5 are equal, thus ensuring the proportionality of the value to the frequency of rotation of the engine shaft, i.e.

about) about g sh Vr K (ism i and id4v)

where K is the proportionality coefficient. The amplitude and frequency of the ripple of the output voltage depends on the frequency a) 0 and the time constant of the integrator 13. In the experimental sample, the ripple frequency of the output signal 1) d4c was (O o / 4.

The device of the proposed electric drive is much simpler known, does not contain analog multipliers and

an adder in the path of the feedback signal conditioner in rotational frequency, as in the prototype. The temperature and temporal error of these nodes reduce the prototype performance indicators and

limit the range of frequency control.

In the device according to the invention, a feedback signal on the rotation frequency is formed in a closed loop of tracking

the value of the period of the input signal. Comparison of this value with that formed in the device is carried out by means of digital (discrete) equipment, which significantly reduces the effect of noise, thermal instability of elements, expands the range of measured rotational frequencies and, accordingly, the range of frequency control of the drive. Simplifying the device improves

reliability.

Claims (1)

The invention AC drive comprising a synchronous motor, on the shaft of which there is a sine-cosine rotary transformer, the input winding of which is connected to the output of the reference frequency generator, frequency converter, outputs connected to the phase terminals of the synchronous motor winding, one control input with the output the first control unit, the other control input - with the output of the rotational speed regulator, whose inputs are connected to the setpoint and date outputs The rotation frequency, the last of which is equipped with a pulse shaper with one input and two outputs, the input of which forms the input of a rotational speed sensor, and an integrator with a reset, the control input of which is connected to one output of the pulse shaper, which is to simplify and extend the frequency control range, the reference frequency generator is provided with a second output, and the sine-cosine rotary transformer is equipped with a second input winding connected to the second output of said generator ora, the output winding of said coupled rotating transfsrmatora  Phie. 2 0 with the inputs of the first control unit and the rotational speed sensor, which is additionally equipped with a three-input pulse width determiner, the first and second inputs connected to the outputs of the pulse former, the threshold element and the second integrator, the output of which forms the output of the rotational speed sensor connected between the output of the above determiner and the input an integrator with a reset, provided with a second input for supplying the bias voltage, the output of the threshold element connected to the input, the output of which is connected n to the third input of the pulse duration determiner. FIEM g Phie. five and anyone's sc UCH J3 Fig.c jL r