SU1160320A1 - Device for measuring current - Google Patents

Description

The invention relates to electrical engineering and is intended to convert and generate analog current feedback signals in control systems with semiconductor converters, carrying out galvanic isolation between the power circuits of the semiconductor converter and control and regulation circuits

The aim of the invention is to improve the measurement accuracy.

FIG. 1 shows a functional diagram of a device for measuring current; in fig. 2 - temporary dia- | 5 grams of the device.

The device contains a measuring shunt 1 connected in the circuit of the measured current in series with the armature winding of the electric motor, two terminals of the shunt 1 are connected to two inputs of the memory integrator 2, the output of which is connected to the first inputs of the comparators 3 and 4 of the pulse width modulator 5, the second inputs of the comparators 3 and 4 combined nd connected to the output of the generator 6 sawtooth voltage, the input of which is connected to the first output of the first pulse shaper and to the memory control input of the memory integrator 2, the input the zeroing control of which is connected to the second output of the first pulse shaper 7, the input of which is connected to the output of the reference frequency generator 9 and the input of the second pulse shaper 10 of the pulse generator 9, the first output of which is connected to the memory control input of the second memory 11, and through the galvanic isolation unit 8, and the second output is connected to the control input reset of the second block 11 of the integrator with memory, the output of the first comparator 3 through the block 12 galvanic decoupling is connected to the first input of the second block 11 integ Memory with memory, the input of which through the third block 13 galvanic isolation is connected to the output of the second comparator 4.

ten

20

25

thirty

35

40

45

50

On the timing diagram (Fig. 2) the following notation is used: 14 - pulses at the output of the reference frequency generator; 15 - the pulse formed at the first outputs of the blocks of the formers 7 and 10 pulses;

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16 - the impulse formed on the second blocks of the formers 7 and 10 pulses; 17- voltage pulse applied to the armature of the electric motor;

18 - pulse shape at the terminals of the shunt T; 19 - the form of voltage at the output of the integrator unit 2; 20 - output generator 6 sawtooth;

21 - the output of the comparator 3; 22 - the output of the integrator unit 11 ·, 23 - the output unit 11.

The device works as follows.

The pulse generator produces | Rectangular pulses 16 with a repetition period T, which synchronizes the operation of the proposed device, and also synchronizes the generator 6 of the sawtooth voltage of the pulse-width modulator 5, which is part of the drive control system (not shown). The pulses 14 from the output of the generator 9 are fed to the input of the shaper 10 short pulses and through the block 8 galvanic isolation - to the input of the shaper 7 short pulses.

At the first output of the first driver 7 and at the first output of the second driver 10, short pulses 15 of the same duration are formed with a period T at time points corresponding to the front pulses 14 of the generator 9.

At the second outputs of the formers 7 and. 10, short pulses 16 of the same duration are formed at the time points corresponding to the pulse decay.

At the moments of receipt of pulses 15 to blocks 2 and 11, storage capacitors are connected to the integrator outputs using analog transistor switches included in the blocks. After the end of the pulses 15, the keys are opened and the recorded information is stored on the storage capacitors until the end of the period T. The pulses 15 are also fed to the input of the generator 6 sawtooth voltage. The pulses 16 after the end of the recording process "close" the zeroing keys of the integrating capacitors in blocks 2 and 11, resulting in a voltage at the outputs of the integrators. becomes zero. Under the action of clock pulses 15, the generator 6 produces a sawtooth voltage

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with period T synchronously and in phase with

sawtooth generator,

part of the drive control system.

Synchronous and common mode operation 5

Sawtooth generators provide a no-beat mode that may occur in the control system. The form of stresses produced by sawtooth generators 1.0

voltage can be any and determined by the design of the generators.

To be specific, in FIG. 2 shows timing diagrams of voltage 20 and generator 6, corresponding to 15 one-sided rising sawtooth voltage.

Starting from the time έο, a pulse voltage 17 is applied to the motor armature. Period 20 of voltage pulse 17 is equal to T, and their duration is set by a pulse-width modulator, which is part of the drive control system. Under the action of 25 pulses 17, a pulsating current occurs in the armature winding of the motor

18. Flowing through the series-connected armature winding and resistive measuring shunt 1, current

18 creates on the shunt 1 a voltage drop, which is fed to the inputs of block 2 of integration and memory. From the moment of time, after 1-2 microseconds _?

'necessary for the census of information and resetting of integrators in blocks 2 and 11, at the output of the block integrator'

2, voltage 19 appears, corresponding to the current integral flowing through shunt 1. By the end of period T at the time point, the output of the integrator of unit 2 will be voltage ’

19, corresponding to the average for the period T value of the current flowing through the shunt 1.

- At time 0, a pulse of sequence 15, “closing” an analog key, connects the storage capacity to the output of the integrator. After the end of the pulse 15 50

a voltage of 20 ( ^q ing) is kept on the storage capacity and on the output of block 2> corresponding to the average

- the value of the motor current for

period T. The impulse 16 of the 55-ti produces "zeroing" of the integrators of blocks 2 and 1 1. After that the integration process is repeated. The voltage from the output to the storage capacity of unit 2 is fed to the inputs of comparators 3 and 4. The other inputs of comparators 3 and 4 receive a sawtooth voltage and _gpn from the output of generator 6. When the voltage is _polarized (Fig. 2), the output of unit 2 is “comparator 3 (at the same time at the output of the comparator 4, the voltage is zero). When the opposite polarity of the voltage at the output of block 2 and, accordingly, the other voltage of the current flowing through shunt 1, the comparator 4 “works”.

At the output of the comparator 3, the voltage is zero. From the point in time to the input of the comparator 3, the voltage from the output of the 2 N _ing block exceeds the sawtooth voltage of the generator 6 (diagram 20). In the code of the comparator 3, a pulse 21 appears, the duration of which is determined by the moment — the voltage of the generator 6 and the voltage of unit 2 are equal. The duration of the pulses 21 is proportional to the average value of the motor current over a period T. 11 integration and memory, to the other input of which from the output of block 13 of the galvanic decoupling receives a zero voltage.

The output pulses of optocouplers in blocks 12 and 13 of galvanic isolation are voltage stabilized using known methods. Starting from time point 0 (after rewriting information and resetting the integrator), the integration process in block 11 takes place. Pulses from the code of block 12 are sent to the non-inverting input of an operational amplifier of block 11 operating in integrator mode. Since the output voltage of the pulses coming from the outputs of block 12 and 13 is stabilized, the voltage 22 on the code of the integrator of block 11 depends only on the duration of the pulses fed to the inputs of the integrator.

When the unit 10 is operating, the pulses from its input are fed to the inverting input of the operational amplifier - the integrator of the unit 11 and the polarity of the voltage at the integrator's output is negative. In the moment

four

five

time, pulse 21 ends and at the output of the integrator of block 11, voltage 22 is proportional to the average value of the motor current over a period T.

8 time point to the memory control input of block 11 a pulse 15 of the sequence arrives and " ¹ * information is memorized

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from the integrator output to the storage capacity. Voltage 23 on the storage capacity remains unchanged during the period T and enters the output bus of the device. At the end of the pulse, an impulse 16, "zeroing out" the integrator, is received at the input of the resetting control of the integrator of the block 11, after which the integration process is repeated.

0

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Claims (1)

MEASURING DEVICE, containing shunt, reference frequency generator, galvanic isolation unit, pulse-width modulator, consisting of a sawtooth voltage generator, two comparators and two galvanic isolation units, characterized in that, in order to improve accuracy, two an integration unit with memory and two pulse shapers, the input of the first pulse shaper. through a galvanic isolation unit, and the input of the second driver is directly connected to the generator output of the standard frequency, the first outputs of the first and second pulse drivers are connected respectively to the first control inputs of the first and second memory integrators, the second outputs of the first and second pulse drivers are connected respectively to the second control inputs of the first and second memory integrators, shunt terminals connected to the two inputs of the first block integration with _pamyatyo} whose output is connected to the first inputs .First and second comparators, the outputs of each of which is connected us respectively through the first and second blocks galvanic decoupling pulse width modulator to the first and second inputs respectively and a second, integration with memory block, the first output of the first pulse shaper is connected via a generator lumber shaped voltage with the second inputs of the first and second comparators ... $ Ц 1160320 >