RU2114507C1 - Method and device for receiving signals transmitted over three-phase power transmission line - Google Patents

Abstract

FIELD: electronics; telemechanics systems using power transmission lines as communication channels without processing. SUBSTANCE: method involves synchronous signal detection to multiplex frequency band allocated for communication channel in three-phase, 0.38, 10, or 35 kV three-phase power transmission line. Device implementing this method has transformer 1, two voltage symmetrical-component filters 2,3, two narrow-band filters 4,5, balanced phase detector 6, mixer 7, low-frequency filter 8, diode bridge 9, differential-frequency filter 10, and phase shifter 11. EFFECT: reduced cost of signal transmission links. 2 cl, 1 dwg

Description

 The invention relates to electrical engineering and can find application in the organization of communication channels along the lines of 0.38-35 kV without high-frequency processing by traps.

 A known method of receiving signals in a three-phase power line, which is implemented in the "System for transmitting and receiving signals through the wires of a three-phase power line" (AS N 1737481, 1992), which is adopted as a prototype. In this method, the signals of the reverse and forward sequences of the first and second frequencies are isolated from a three-phase power line, the frequency data is filtered out and the signals are processed in a known manner.

 The disadvantage of this method of receiving signals is low noise immunity. The "System for transmitting and receiving signals through the wires of a three-phase power line", which implements the known method, has the same drawback.

 The proposed method for receiving signals in a three-phase power line and a device for its implementation solves the problem of increasing noise immunity.

 A signal receiving device in a three-phase power line (see drawing) contains a transformer 1, two voltage filters of symmetrical components 2, 3, two narrow-band filters 4, 5, a balanced phase detector 6, a mixer 7, a low-pass filter 8, a diode bridge 9, a filter differential frequency 10, phase shifter 11.

 A device for receiving signals in a three-phase power line operates as follows.

The voltage and signals of the negative sequence U ₂ (f ₁ ) at a frequency F ₁ and the voltage of a direct sequence U ₁ (f ₂ ) at a frequency f ₂ are formed on the low-voltage windings of the network transformer 1, and f ₂ - f ₁ = 2F Hz. The first filter 2 of the voltage of the symmetrical components of the negative sequence is tuned to the frequency f ₁ , the second filter 3 of the voltage of the symmetrical components of the negative sequence is tuned to the frequency F ₂ . From the outputs of the first and second filters 2 and 3, the voltages go to the inputs of the first and second narrow-band filters 4 and 5. From the outputs of the first and second narrow-band filters 4 and 5, voltages of frequencies f ₁ and f ₂ are applied to the inputs of the first balanced phase detector 6.

Let the output voltage of the first narrow-band filter 4 have the signal voltage
U ₁ (t) = U _m1 cos (ω ₁ t + φ ₁ ) (1).

.From the output of the second narrow-band filter 5 we have a signal voltage
U ₂ (t) = U _m2 cos (ω ₂ t + φ ₂ ) (2),
Where

.

 This follows from the principle of operation of a passive-active type transmitter.

где
U_m - амплитудное значение напряжения биений.Due to the fact that the power source of such transmitters is a three-phase electric network, the voltage of which is F, voltage of signals of two frequencies f ₁ and f ₂ are formed in the line, separated by an amount of Ω = 2π2F Hz, i.e. beats form. Phase voltage (e.g. phase A) is

Where
U _m - the amplitude value of the voltage of the beats.

At t = 0, the transmitter at the transmission point (not shown in the drawing) does not work. At the receiving point there are no voltage signals U ₁ (t) and U ₂ (t) described by expressions (1) and (2).

,
где
U_m1 и U_m2 - амплитудные значения напряжений сигнала на входах первого балансного фазового детектора 6;
K_g - коэффициент передачи амплитудного детектора;
φ_c= (ω₁-ω₂)t+φ₁-φ₂ (5) ,
где
ω₁= 2πf₁ ω₂= 2πf₂ (6)
Причем выполняется условие:
f₁=f_c-F, f₂=f_c+F
где
f_c - частота коммутации ключа передатчика, установленного в пункте передачи (на чертеже не показан):
F - частота промышленного напряжения.At t> 0, the transmitter at the transmission point starts to work. At the reception point, voltages U ₁ (t) and U ₂ (t) appear, which are supplied to the first and second inputs of the balanced phase detector 6, from the output of which the signal voltage U _c (t) is supplied to the first input of the mixer 7, and

,
Where
U _m1 and U _m2 are the amplitude values of the signal voltages at the inputs of the first balanced phase detector 6;
K _g is the gain of the amplitude detector;
φ _c = (ω ₁ -ω ₂ ) t + φ ₁ -φ ₂ (5),
Where
ω ₁ = 2πf ₁ ω ₂ = 2πf ₂ (6)
Moreover, the condition is satisfied:
f ₁ = f _c -F, f ₂ = f _c + F
Where
f _c - switching frequency of the transmitter key installed in the transmission point (not shown in the drawing):
F is the frequency of industrial voltage.

In view of expressions (5) and (6), expression (5) has the form:
U _c = -Ωt (8).

.In view of (7), expression (4) has the form:
U _c (t) = A _mc CosΩt (9),
Where

.

The voltage U _c (t) is supplied to the first input of the mixer 7.

,
где
U_mF - амплитудное значение фазного напряжения промышленной частоты.The voltage at the output of the diode bridge 9 U (t) _{9 is} described by the expression

,
Where
U _mF is the amplitude value of the phase voltage of the industrial frequency.

 A useful signal is the voltage of the second harmonic of the frequency F, which is the voltage of the difference frequency.

,
где

K - коэффициент затухания в фильтре 10;
φ - начальный сдвиг фазы.The voltage at the output of the filter of the difference frequency 10 U (t) _{10 is} described by the expression:

,
Where

K is the attenuation coefficient in the filter 10;
φ is the initial phase shift.

The voltage at the output of the phase shifter 11 is the local oscillator voltage U (t) _r , which is described by the expression:
U (t) _r = A _mg cosΩt (12),
Where
A _mr is the amplitude value.

 From (12) it follows that the frequency and phase of the local oscillator voltage coincides with the frequency and phase of the voltage of the differential frequency according to (9).

The voltage U (t) _{r is} supplied to the second input of the mixer 7.

,
где
m < 1 - постоянный коэффициент:
S₀ - крутизна характеристики нелинейного элемента смесителя 7.The voltage at the output of the mixer U (t) _{cm of the} multiplier will be equal to:

,
Where
m <1 - constant coefficient:
S ₀ - the steepness of the characteristics of the nonlinear element of the mixer 7.

. (14)
Для выделения постоянного напряжения U₀ напряжение с выхода смесителя 7 поступает на фильтр 8 нижних частот, который отфильтровывает напряжение с частотами Ω и 2Ω.
Использование данного способа обработки сигналов является синхронным детектированием. Анализ работы синхронного детектора показывает, что выполненное им преобразование сигналов соответствует одной из операций оптимальной обработки сигналов.An analysis of expression (13) shows that the first and second terms are voltages having frequencies Ω and 2Ω. The last term is a constant voltage:

. (fourteen)
To select a constant voltage U _{0, the} voltage from the output of the mixer 7 is supplied to a low-pass filter 8, which filters the voltage with frequencies Ω and 2Ω.
Using this method of signal processing is synchronous detection. An analysis of the operation of the synchronous detector shows that the signal conversion performed by it corresponds to one of the operations of optimal signal processing.

 Achievement of the technical result - increased noise immunity is achieved by increasing the signal-to-noise ratio by 2 times with this signal processing.

Claims (2)

1. The method of receiving signals in a three-phase power line, which consists in distinguishing from a three-phase power line signals of the reverse and forward sequences, respectively, of the first f ₁ and second f ₂ frequencies, while the condition f ₂ -f ₁ = 2F is fulfilled, where F is frequency supply voltage, characterized in that the first mixed signals f ₁ and f ₂ of the second frequency, the difference frequency f recovered ₂ -f ₁ is rectified phase voltage three-phase power transmission line, the second filtered phase 2F garomoniku rectified voltage COMPENSATION ruyut phase shift of the second harmonic phase of the rectified voltage, which is detected synchronously with the voltage difference frequency.  2. A device for receiving signals in a three-phase power line containing a network transformer, the first and second voltage filters of the symmetrical components, the inputs of each of which are connected to the corresponding low-voltage windings of the network transformer, and the outputs of the first and second voltage filters of the symmetric components are connected to the inputs of the first and second narrow-band filters, characterized in that a balanced phase detector, a mixer, a low-pass filter, a rectifying diode mo t, a difference filter, a phase shifter, the outputs of the first and second narrow-band filters are respectively connected to the first and second inputs of a balanced phase detector, the output of which is connected to the first input of the mixer, the output of which is connected to the input of the low-pass filter, the input diagonal of the rectifier diode bridge is connected by any phase and "ground", the output diagonal of which is connected to the input of the differential frequency filter, the output of which is connected to the input of the phase shifter, the output of which is connected to the second input of the mixer.