SU1619176A1 - Apparatus for measuring speed of two-speed induction motor - Google Patents

Abstract

The invention relates to the measurement and control of motion parameters and can be used to measure the angular velocity of asynchronous motors, in particular two-speed asynchronous motors with a short-circuited rotor and two independent stator windings. The aim of the invention is to improve the reliability and accuracy of measurement. A device for measuring the speed of the asynchronous motor 1 comprises a signal extraction unit 2 and a measurement unit 3 connected to the output of the separation unit. The device is equipped with a power switching unit 4 and a control unit 5, the signal extracting unit 2 comprising a switching element unit 6, a pulse shaping unit 7, a control unit 8 and a logic block 9, the output of which is the output of the signal extracting unit 2. The signal extracting unit 2 processes the EMF signals arising in the disconnected winding of the engine 1 and generates a pulse signal whose frequency is proportional to the angular velocity of the engine 1, measured by the measuring unit 3. 2 hp ff. 3 il.

Description

i

 G f lg

eight

1

The invention relates to the measurement and control of motion parameters and can be used to measure the angular velocity of a two-speed asynchronous motor with a short-circuited rotor and two independent stator windings.

The purpose of the invention is to increase the reliability and accuracy of speed measurement.

FIG. 1 shows a diagram of a device for measuring the speed of a two-speed asynchronous motor: FIG. 2 is a diagram of a signal generation unit; on fig.Z - block control scheme.

The device (Fig. 1) contains a two-speed asynchronous motor 1, a signal extraction unit 2 and a measurement unit 3 connected to, the motion of unit 2, blocks of power switching elements 4 and control 5, the signal extraction unit 2 containing blocks of switching elements 6 , forming pulses 7, control 8 and logic 9, the output of the latter is the output of the signal extracting unit 2, the first inputs of the power switching unit 4 are connected to a power source, the first and second outputs of the switching power supply unit 4 are connected to Vym and second inputs of asynchronous motor 1, which are the outputs of high and low speed windings, and are connected respectively to the first and second inputs of the block 6 of switching elements, the third and fourth inputs of which are connected to the first and second outputs of the control block 5, which are connected respectively to the second and the third inputs of the block 4 of the power switching elements, the first three outputs of the block 6 of the switching elements are connected respectively to the first three inputs of the pulsing unit 7, the first mp / i of the output of which connected to the first three inputs of the control unit 8, the output of which is connected to the second input of the logic block 9, the first input of which is connected to the fourth output of the pulse shaping unit 7. The latter (FIG. 2) contains three identical formation channels and a pulse summing circuit 10, each shaping channel containing a series-connected amplifier 11, a filter 12, a comparator 13 and a pulse shaper 14, the output of which is connected to the corresponding input of the pulse summing circuit. The control unit 8 contains three D-flip-flops 15-17, the D-inputs of which are connected respectively to the three inputs of the control unit. The output of the first D-flip-flop 15 is connected to the R-input of the second, and the output of the second D-flip-flop 16 is connected to the R-input of the third, the output of which is the output of the control unit. RS-inputs of the first D-flip-flop and S-inputs of the second and third through a resistor

RIs are connected to the power rail. The C input of the first D flip-flop is connected to the second input of the control unit, and the C inputs of the second and third inputs, respectively, with the third and first inputs of the control unit.

The essence of the technical solution is based on physical processes occurring in a real asynchronous machine, concluding that in an asynchronous motor, besides the working harmonic flow, there are higher harmonic currents of the stator and the rotor of the order of v and i. The main reasons for the occurrence of these harmonics are the discrete arrangement of the windings in the grooves, the effect of the stator slots

and rotor on the magnetic field of the working harmonic. The harmonics dominated by harmonics generated by the rotor current of the fundamental frequency

25

f2 sfl.

(one)

where fa is the frequency of the rotor currents; f t is the frequency of the stator currents; S - scanning. 30 The length of this harmonic is the rotor floor.

 + 1,

(2)

where 7.2 is the number of slots of the rotor;

P is the number of poles of the working winding;

“2 is any integer.

Frequency of currents induced by these harmonics in the stator

) 0 S) -fi. (3)

In view of (2), expression (3) has the form

45

 + §-K2 (1-S) -fi.

(four)

In a two-speed asynchronous motor with a squirrel cage rotor and two

by independent stator windings, when one of them is connected to the power source, the second one can be used as a measuring one. Since in a two-speed motor, the electrical axles

Since windings with different numbers of poles are shifted by 90 degrees, then when one winding is operated in another, there is no EMF due to the working harmonic field, and only the EMF of higher harmonics is induced. The spectrum is dominated by the harmonic rotors of the rotor, the order of which is determined by the expression (2) with Ka 1. Since the axes of each phase of the respective stator windings are shifted 120 degrees grad.of EMF signals induced in each phase of the disconnected stator winding form a three-phase system alternating voltages shifted by 120 hectares, the phase rotation order of which is determined by the direction of rotation, and the frequency is proportional to the angular velocity of the rotor.

Each channel of the pulse shaping unit converts the harmonic signal of the induced EMF with frequency f "into a pulse sequence whose frequency fi 2 fyu. The outputs of each channel are fed to the summation circuit whose output signal has frequency b f".

In the initial state, there are no signals at the first and second outputs of the control unit 5. The first and second inputs of the asynchronous 2-speed motor 1, which are the leads of the high and low speed windings, are disconnected by the power switching unit 4 from the power source. The first three inputs of the pulse shaping unit 7 are disconnected from the windings of the asynchronous motor 1 by the block 6 of switching elements. There are no signals at the fourth output of the pulse shaping unit 7 and the output of the logic block 9, in addition, the control unit 8 generates a signal at the output that prohibits the arrival of signals from the fourth output of the pulse shaping unit 7 to the input of the measurement unit 3.

When the control unit 5 forms a motor acceleration command, a signal arrives at its first output, which arrives at the second input of the power switching unit 4 and the third input of the switching elements block b. Unit 4 of the power switching elements connects the first inputs of the asynchronous motor 1, which are the leads of the high speed winding, to the source of alternating voltage. The block b of switching elements provides the connection of the second inputs of the asynchronous motor 1, which are the leads of the low speed winding, to the first three inputs of the block 7 of formation of pulses. In the windings of low speed, the motor 1 induces an emf of higher harmonics, which are fed to the first three inputs of the pulse shaping unit 7. In the latter, signals from the first three inputs go to three identical channels of formation.

In each channel, the signals from the inputs of the pulse shaping unit 7 are fed to the first two inputs of the amplifier t1, having a constant gain factor. The amplified signal from the output of amplifier 11 is fed to a filter 12, which suppresses the low-frequency components in the EMF signal. The comparator 13, connected to the output of the filter 12, generates a pulse signal from the harmonic input signal, switching from one state to another when the input signal goes to zero. The output signal of the comparator 13 is fed to the input of the imaging unit 14 pulses and

5, the second output of each formation channel. A shaper of 14 pulses at the front and in the decay of the input signal generates pulses of constant amplitude and constant duration, which arrive at

0 first outputs of each channel. The signals from the first outputs of each formation channel are fed to the inputs of the pulse summing circuit 10. The signals at the input of each channel are shifted by 120 al.

5, therefore, the frequency of the signal at the output of the summing circuit 10 is six times higher than the frequency of the input signals of the pulse shaping unit 7. The signals from the second outputs of each channel of the formation are fed to

0 inputs of the control unit 8, which controls the sequence of the phase alternation of the converted input signal of the pulse shaping unit 7. If the valid order matches

5 the phase alternation with the required control unit 8 generates a signal by which the logic unit 9 provides the passage of the signal from the fourth output of the pulse shaping unit 7 to the input of the unit 3 measurements.

In the zone of low angular velocities in the spectrum of the induced emf signal, there is no predominance of the rotor harmonics of the tooth order as compared to other higher harmonics, and the frequency of the output signals

5 of the pulse shaping unit 7 does not correspond to the actual speed of the engine 1. The control unit 8 generates a signal at the output, according to which the logic block 9 prevents the arrival of signals to

0 block input 3 measurements. A similar signal by the control unit 8 also forms, in case of a mismatch of the direction of rotation of the motor, to a predetermined order of alternation of the phases of the supply voltage 5. When a signal for deceleration appears at the second output of the control unit 5, the power switching elements unit 4 disconnects the first and connects the second inputs of the asynchronous motor 1 to the power source. Block 6 switching elements

It provides the connection of the first inputs of the motor 1, which are the leads of the disconnected high speed winding, to the inputs of the pulse shaping unit 7. The operation of the remaining units and units of the device does not change.

Claims (3)

1. An apparatus for measuring the speed of a two-speed asynchronous motor, comprising a signal extracting unit and a measuring unit connected to the output of the signal extracting unit, characterized in that, in order to increase the reliability and accuracy of the measurement, it is equipped with a power and switching unit and a control unit , while the first inputs of the power switching unit are connected to a power source, the first and second outputs of the power switching elements are connected to the first and second inputs of the asynchronous motor and the signal extraction unit is designed as a unit of switching elements, the phase outputs of which are connected to the phase inputs of the pulse shaping unit, the phase outputs of which are connected to the phase inputs of the control unit, the output of which and the fourth output of the pulse formation unit are connected which is the output of the signal extractor, the first and second inputs of the asynchronous motor are connected respectively to the first and second inputs The block of switching elements, the third and fourth inputs of which are connected to the first and second outputs of the control unit, which are connected respectively to the second and third inputs of the power switching unit. 2. Pop-1 device, characterized in that the pulse shaping unit contains the same-identical formation channel and the pulse summing circuit, with the 1st input of the summing circuit connected to the first output of the 1st formation channel, the second output of the 1st channel is connected to The i-th output of the pulse shaping unit, the fourth output of which is connected to the output of the pulse summing circuit, the first input of the 1st formation channel is connected to the 1st input of the pulse shaping unit, the second inputs of the first, second and third channels are connected with the second, third and first inputs of the pulse shaping unit. 3. The device according to claim 2, characterized in that each channel of the formation contains a series-connected amplifier, filter, comparator and pulse shaper, the output of which is connected to the first output of the formation channel, the output of the comparator is connected to the input of the pulse shaper and the second output of the channel formation, the first and second inputs of the amplifier are connected respectively to the first and second inputs of the formation channel. FIG. 2 FIG. J