RU2469392C1 - Device for potential separation of dc circuits - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: device comprises an amplifier - limiter, an amplitude modulator with transformer separation of an "input-output" circuit, a summator, an integrator, a relay element, a unit of a logical function "Equivalence", a frequency divider, a separation transformer, a rectifier (demodulator).

EFFECT: improved accuracy of device operation and reduction of weight and dimensional indices.

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Description

The invention relates to the field of analog computing and can be used in control systems for the automation of technological processes.

A device for potential separation of direct current circuits (UPR), containing a modulator, demodulator, isolation transformer, output smoothing filter, a carrier oscillator for controlling the keys of the modulator and demodulator (Terekhov V.M. Elements of an automated electric drive. - M .: Energoatomizdat, 1987 . - 225 p.).

The known device is characterized by low accuracy, as it belongs to the class of open control devices, where the drift of the parameters of any of the functional elements of the circuit causes a significant error in the conversion of the input signal.

It is known UPR containing an integrator, relay elements, optoelectronic switches, filter (SU No. 1141424 G06G 7/12. Decl. 17.03.83, publ. 23.02.85, Bull. No. 7).

The disadvantage of this control is the low speed, limited by the switching time of the optoelectronic pairs, and the need for an additional power supply of the input integrating stage, which reduces the reliability of the control in general.

Closest to the proposed device is the control unit, which contains an amplitude modulator, adder, integrator, relay element, frequency divider, a block of logical functions "Equivalence", input and output terminals (Gafiyatullin R.Kh., Tsytovich L.I., Tsytovich P.L. Deployment converter with potential separation of direct current circuits // Instruments and experimental equipment. - M.: RAS. 1997. - No. 3. - P.85-88).

The prototype device belongs to the class of integrating deploying converters with frequency-pulse-width-pulse modulation and implements the principle of developing converting with out-of-phase adjacent cycles (Tsytovich L.I. Deploying converters for control systems of valve electric drives and technological automation. Thesis ... Doct. Chelyabinsk: ChSTU, 1996 .-- 464 p.)

The disadvantage of the UPR prototype is the low accuracy in the field of "large" signals, when the frequency-pulse-width modulation frequency of the carrier oscillations is significantly reduced. This causes the saturation mode of the isolation transformer of the amplitude modulator and the transition of the control unit to the state of infra-low-frequency oscillations with a simultaneous decrease in the transmission coefficient with respect to the input signal. In addition, when the individual elements of the circuit are powered from sources connected to a 50 Hz network, the overall dimensions of the control system can significantly increase.

The invention is based on a technical problem, which consists in increasing the accuracy of the device for the potential separation of direct current circuits and reducing its overall dimensions.

The proposed device for potential separation of DC circuits contains an input signal source, an amplitude modulator, the output of which is connected to the first input of the adder, the output of which is connected to the input of the integrator, the output of the integrator is connected to the input of the relay element, the output of which is connected to the first input of the block ", To the second input of the adder and to the input of the frequency divider, the output of which is connected to the second input of the block of the logical function" Equivalence "and to the first input of amplitudes modulator, the output of the block of the logical function "Equivalence" is connected to the output terminal of the device and is characterized by the fact that it has an amplifier-limiter, a rectifier (demodulator) and an isolation transformer, the input of the amplifier-limiter connected to the input signal source, and the output connected to the second inputs of the amplitude modulator, the input of the isolation transformer is connected to the output of the frequency divider, and the output is connected to the input of the rectifier (demodulator), the output of which is connected to the pit voltage terminal limit amplifier.

The technical result of the proposed device is its increased accuracy in operation and reduced overall dimensions.

The stated technical problem is achieved due to the power supply of the amplifier-limiter with the rectified voltage of the carrier frequency of self-oscillations of the UPR and the limitation of the voltage level supplied to the input of the amplitude modulator due to the amplifier-limiter connected between the input signal source and the information input of the amplitude modulator. At the same time, the “saturation” of isolation transformers and, as a result, the infra-low-frequency “beats” of the average value of output pulses in the region of “large” signals is eliminated in the control unit. In addition, the power of the amplifier-limiter from the isolation transformer connected to the output of the frequency divider ', can dramatically reduce the overall dimensions of the device due to the high frequency of the carrier oscillations of the control gear.

The invention is illustrated by drawings, where:

figure 1 - is a structural diagram of the proposed device;

figure 2-4 shows a timing diagram of the signals and characteristics of the device.

The structure of the device (Fig. 1) includes serially connected input signal source - input terminal 1, amplifier-limiter 2, amplitude modulator 3, adder 4, integrator 5 and relay element 6. The output of relay element 6 is connected to the first input of the logic function block " “Equivalence” 7, to the second input of the adder 4 and to the input of the frequency divider 8. The output of the frequency divider is connected to the second input of the block of the logic function “Equivalence” 7, with the input of the amplitude modulator 3 and with the input of the isolation transformer 9. The output will split ceiling elements transformer 9 is connected to the input rectifier (demodulator) 10, whose output is connected to a terminal of the voltage amplifier power limiter unit 2. The output logic function "equivalence" 7 is connected to an output terminal of the device 11.

Amplifier-limiter 2 has a linear characteristic with a saturation zone ± X _KR . In general, it can be both inverting and non-inverting. The amplitude modulator 3 generates an alternating pulse signal at the output, the amplitude of which corresponds to the input action at terminal 1, and the frequency is determined by the frequency of the output voltage of the frequency divider 8. The sign of the output pulse of the amplitude modulator 3 corresponds to the product of the signs of the signals from the output of the amplifier-limiter 2 and frequency divider 8. Amplitude modulator 3 is implemented according to a transformer circuit that provides a potential separation of the input-output channel of the control unit.

The integrator 5 is made with a transfer function W (p) = 1 / T _And p based on the operational amplifier. When applying a “jump” of the input signal, the output voltage of the integrator 5 changes linearly in the direction opposite to the sign of the input action.

Relay element 6 has a non-inverting hysteresis loop and switching thresholds ± b symmetrical with respect to the zero level. Its output voltage varies discretely within ± A.

The frequency divider 8 (counting trigger) is implemented with a division ratio of 2.0, and its output pulses have an amplitude of ± A.

Block 7 performs the logical function "Equivalence". The signal at its output has a + A level when the signs of the input signals coincide and a value of -A when the signs of these signals do not match.

In the future, we assume that the transfer coefficient of the amplifier-limiter 2, the amplitude modulator 3, the rectifier (demodulator) 10, and the isolation transformer 9 is equal to one, the pulses at the output of the relay element 6, the frequency divider 8, and the block of the logic function "Ambiguity" 7 vary discretely within ± A, and the signal at the output of amplifier-limiter 2 in sign corresponds to the input signal at terminal 1 (it should be noted that the inverting or non-inverting character of the static characteristic of amplifier-limiter 2 does not have intsipialnogo values in terms of the principle of operation of the device, and only affects the appearance of the static characteristic NRM (inverting or noninverting characteristic "input-output" RVP).

The principle of operation of the device is as follows.

The device (figure 1) belongs to the class of deploying integrating converters with antiphase adjacent cycles of the deploying conversion. At a zero level of the input signal X _BX (Fig. 2a, t <t ₀ ), the signal Y _A (t) at the output of the amplifier-limiter 2 and the amplitude modulator 3 is absent (Fig. 2b) and the average value of the pulses Y _P (t), Y _OUTPUT (t) at the output of the relay element 6 and the block of the logical function "Equivalence" 7 for the sampling interval T ₀ is equal to zero (pigv, d).

(фиг.2в) темп развертки Y_И(t) с выхода интегратора 5 определяется разностью выходных сигналов амплитудного модулятора 3 и релейного элемента 6 и в интервале

- суммой этих сигналов. Здесь:

- нормированное значение порогов переключения релейного элемента 6;

- нормированное значение входного сигнала на входной клемме 1; ±А - амплитуда выходных импульсов релейного элемента 6 и блока логической функции «Равнозначность» 7.When the input signal is applied (Fig. 2a, t≥t ₀ ), rectangular pulses Y _A (t) are formed at the output of the amplitude modulator 3 with an amplitude equal to ± X _BX and with the frequency of the output signal Y _PM (t) of the frequency divider 8, driven a self-oscillating circuit formed by an amplitude modulator 3, an adder 4, an integrator 5 and a relay element 6 (fig.2b-d). In the interval

(figv) the scan rate Y _AND (t) from the output of the integrator 5 is determined by the difference of the output signals of the amplitude modulator 3 and the relay element 6 and in the interval

- the sum of these signals. Here:

- the normalized value of the switching thresholds of the relay element 6;

- normalized value of the input signal at input terminal 1; ± A is the amplitude of the output pulses of the relay element 6 and the block of the logical function "Equivalence" 7.

After the completion of the cycle t ₁₁ + t ₂₁ (Fig.2c), the frequency divider 8 is switched (Fig.2d) and the sign of the signal changes at the output of the amplitude modulator 3 (Fig.2b). As a result, the next transformation cycle t ₂₂ + t ₁₂ adjacent to t ₁₁ + t ₂₁ has the parameters t ₁₂ = t ₁₁ , t ₂₁ = t ₂₂ and is oriented out of phase with respect to the sign of the pulses relative to the previous cycle t ₁₁ + t ₂₁ . When demodulating the output signal of the relay element 6 using the "equivalence" function, a pulse-frequency-pulse signal with a constant component is generated at the device output (terminal 11)

,

,

- период выходных импульсов блока логической функции «Равнозначность» 7. Полоса пропускания устройства при

соответствует величине

.proportional to the input signal X _BX (fig.2d, e), where

- the period of the output pulses of the block logical function "Equivalence" 7. The bandwidth of the device when

corresponds to

.

Consider the effect of the “zero” offset signals Δе of the amplitude modulator 3 and integrator 5, which have the greatest effect on the error level of the average value of the output signal of the device. We believe that the error Δе is generalized, takes into account the instability of the characteristics of the amplitude modulator 3 and integrator 5, is applied to the input of the adder 4 (Fig. 1), and in sign, for example, coincides with the sign of the input action X _BX (Fig. 3a, b).

In intervals

(Fig. 3c), the signal Δе will lead to a change in the durations of the "half-cycles" of the deployment transform t ₂₁ and t ₁₁ . The intervals t ₂₂ and t ₁₂ increase to values

и

and

,

- коэффициенты передачи сигнала Δе под действием входного сигнала на выход блока логической функции «Равнозначность» 7;

- нормированное значение сигнала Δе (фиг.3г).respectively, where:

,

- transmission coefficients of the signal Δе under the action of the input signal to the output of the block of the logical function "Equivalence"7;

- the normalized signal value Δе (figg).

As a result, for the sampling interval

, а относительная ошибка преобразования устройства составитpulses Y _p (t) (pigv) their constant component is equal to

, and the relative error of the device conversion will be

.

.

. Учитывая, что

, дрейф «нуля» выходного сигнала устройства намного ниже, чем в типовых структурах.It is noteworthy that, in comparison with traditional devices for potential separation of direct current circuits, for example, of the “modulator - demodulator” type in the device under consideration, the influence of the signal Δе is multiplicative (dependent on the level of X _VX ), the nature of the error the device is completely absent at X _BX = 0, and with an increase in the input signal is determined by the value

. Given that

, the drift of the “zero” output signal of the device is much lower than in typical structures.

The disadvantage of this class of device is the low accuracy in the field of "large" signals. The reason is that with an increase in the input signal in the self-oscillating path formed by the adder 4, the integrator 5 and the relay element 6 of the control unit decreases the frequency of the carrier oscillations. As a result, the isolation transformer of the amplitude modulator 3 is “saturated” and the value of its transfer coefficient decreases, which entails the transition of the control switch to the low-frequency “beat” mode of the average value of the output pulses. Consider this mode based on the timing diagrams of the signals shown in figure 4.

(фиг.4б, в, область «А»). При этом из-за «насыщения» трансформатора амплитудного модулятора 3 падает его коэффициент передачи, что влечет за собой снижение уровня сигнала, поступающего на вход сумматора 4. Тогда частота несущих колебаний УПР вновь возрастает (фиг.4б, в, области «В», «С»,

). Повышение частоты несущих автоколебаний выводит разделительный трансформатор амплитудного модулятора 3 из состояния «насыщения», что восстанавливает его коэффициент передачи. Это в свою очередь вновь вызывает снижение частоты автоколебаний УПР (фиг.4б, в, области «D», «Е») и спад коэффициента передачи прямого канала преобразования УПР. В дальнейшем процесс периодически повторяется, носит инфранизкочастотный характер (фиг.4г), определяемый постоянной времени разделительного трансформатора, и приводит к результирующему снижению коэффициента усиления УПР в области «больших» сигналов Х_ВХ≥Х_КР (фиг.4д).Suppose that the critical amplitude of the input signal, at which there is a "saturation" of the magnetic circuit of the transformer of the amplitude modulator 3, is the value of X _KP (figa). When the condition X _BX ≥X _KR (Fig. 4a, t≥t ₀ ) is fulfilled, the frequency of the output pulses of the relay element 6 and the control unit as a whole sharply decreases, which accordingly entails a decrease in the frequency of the output signal of the frequency divider 8 to

(figb, c, region "A"). In this case, due to the "saturation" of the transformer of the amplitude modulator 3, its transmission coefficient decreases, which entails a decrease in the level of the signal supplied to the input of the adder 4. Then, the frequency of the carrier oscillations of the control amplifier increases again (Fig. 4b, in the region "B", "FROM",

) Increasing the frequency of the carrier self-oscillations removes the isolation transformer of the amplitude modulator 3 from the state of "saturation", which restores its transmission coefficient. This, in turn, again causes a decrease in the frequency of self-oscillations of the UPR (Fig. 4b, in the region “D”, “E”) and a decrease in the transmission coefficient of the forward channel of the UPR conversion. In the future, the process is periodically repeated, it has an infra-low-frequency character (Fig. 4d), determined by the time constant of the isolation transformer, and leads to a resulting decrease in the gain of the control amplifier in the region of "large" signals X _BX ≥X _KR (Fig. 4d).

Obviously, to eliminate this drawback, it is sufficient to limit the signal at the input of the amplitude modulator 3 to the level X _BX <X _KR , which is implemented in the proposed device using the amplifier-limiter 2, having, for example, the static characteristic shown in Fig.4e, where Δ is an infinitesimal quantity. If Х _ХВ on terminal 1 exceeds the permissible value, then the output signal of the amplifier-limiter 2 does not exceed the critical level X _КР , thereby excluding the transition of the control switch to the low-frequency beat mode of the coordinate Y ₀ .

To power the amplifier-limiter 2, it would be possible to use an autonomous voltage source, galvanically separated from the power supply of the UPR. However, such a technical solution is unacceptable in the framework of this device for the following reasons. When using an autonomous power supply, the ripple frequency of its output signal, regardless of the stabilization coefficient of the stabilizer, is constant and is determined by the frequency of the mains voltage. The frequency of self-oscillations of the UPR "floats" depending on the level of the converted signal. Under these conditions, it is possible to “superimpose” two frequencies from the self-oscillating path of the UPR and the autonomous power supply of the amplifier-limiter 2, which will lead to the appearance of additional low-frequency harmonics in the output signal of the UPR when allocating the average value of its output pulses.

The elimination of this potential drawback of the control loop can be achieved if the frequency of the carrier self-oscillations is aligned with the ripple frequency of the power supply of the amplifier-limiter 2. To this end, the output of the transformer 9 is connected to the output of the frequency divider 8. This allows you to get an alternating signal with a self-oscillation frequency on the secondary side of the isolation transformer 9 UPR. As a result, at the output of the rectifier (demodulator) 10, a constant power supply voltage of the amplifier-limiter 2 is formed with a ripple frequency dependent on the level of the input signal of the control amplifier. This eliminates the operation of the control amplifier with the formation of additional low-frequency harmonics due to the "superposition" of two non-multiple frequencies to each other. In addition, taking into account the high value of the self-oscillation frequency of the UPR (tens of kHz), the overall dimensions of the isolation transformer 9 are sharply reduced compared to the case when the power of the amplifier-limiter 2 would be produced according to the traditional scheme from a source connected to a network voltage of 50 Hz.

Thus, the proposed technical solution differs from the known increased accuracy in the field of "large" signals and low weight and size indicators.

The considered device is supposed to be used in the control system of the electric drive complex for the large-diameter pipe finishing section of workshop No. 6 of ChTPZ OJSC to transmit signals to the control computer that characterize the state of power converters, executive electric motors, and technological mechanisms. The estimated economic effect of the introduction of the entire complex of equipment is 120-180 thousand rubles. in year.

Claims (1)

A device for potential separation of direct current circuits containing an input signal source, an amplitude modulator, the output of which is connected to the first input of the adder, the output of which is connected to the integrator input, the integrator output is connected to the input of the relay element, the output of which is connected to the first input of the block ", To the second input of the adder and to the input of the frequency divider, the output of which is connected to the second input of the logic function block" Equivalence "and to the first input of the amplitude module torus, the output of the block of the logical function "Equivalence" is connected to the output terminal of the device, characterized in that it has a limiter amplifier, a rectifier (demodulator) and an isolation transformer, while the input of the amplifier-limiter is connected to the input signal source, and the output is connected to the second input of the amplitude modulator, the input of the isolation transformer is connected to the output of the frequency divider, and the output is connected to the input of the rectifier (demodulator), the output of which is connected to the terminal of the power supply voltage of the amplifier limiter.

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