RU143538U1 - DEVICE FOR ANALOGUE POWER COEFFICIENT SENSOR - Google Patents

Abstract

An analog device of a power factor sensor, which contains a pulse-phase, amplitude converter, current transformer and voltage transformer, characterized in that for any form of current from the load resistor of the intermediate current transformer, the voltage is supplied to two low-pass filters in series in the current channel to isolate the voltage the first harmonic, which is fed to the high-pass filter, after which the voltage is simultaneously applied to the phase-shifting device and to the compar a torus that inverts in the current channel from a phase shifter, the voltage is applied to a comparator that does not invert in the current channel, positive components of rectangular pulses are extracted from both comparators, which are normalized by logic elements and fed to the inputs of an exclusive OR, the output of which is connected to the inverter on the AND element NOT, from which short pulses are supplied to the base of the pulse-phase, amplitude converter, from the voltage transformer an alternating voltage is supplied to the input of the comparator, not voltage in the channel, from which rectangular polarity impulses are supplied to the integrator, the voltage of which is triangular in shape is applied to two low-pass filters in series in the voltage channel to obtain a reference sinusoidal voltage, then the voltage is supplied to the phase shifter, from which this voltage is supplied to the precision rectifier , from which voltage is supplied to the collector of a pulse-phase, amplitude converter, the output of which is connected to a constant filter

Description

The utility model relates to measuring equipment devices and can be used as a power factor sensor for automation and telemechanization of the parameters of the load node of the power supply system.

Power factor is one of the main energy characteristics of consumers of electric energy.

A power factor sensor is also needed for more precise control and regulation of the temperature of induction heating plants.

In industry, and especially for driving centrifugal pumps in oil production, frequency-controlled electric drives are increasingly being used. Frequency converters are made with an intermediate DC link - these are either diode rectifiers or thyristor converters. The current phase of the primary winding of the power transformer is pulsed with pauses, rectangular unipolar in two-stroke and rectangular unipolar in single-cycle (three-phase zero) rectification schemes. This causes problems in measuring the power factor. To design the sensor, it is advisable to isolate the first harmonic from the current pulses. In addition to the accuracy of the signal value, the sensor is required to have high speed, linear output characteristics with an allowable ripple coefficient of the output voltage, which is achieved by maximizing the use of the useful signal in each half-wave of a sinusoid with a frequency of 100 Hz.

The source of the analogue (A.Yu. Balzamov, A.N. Polivtsev, Single-phase power factor meter. "Mordovian State University named after NP Ogarev. E-mail: mailto: balsamovau@mrsu.ru) describes the developed device, whose structural diagram is shown in Fig. one.

“As a basis for constructing the measuring part of the device, it is convenient to use the specialized ADE7753 microcircuit from Analog Devices, a precision electric meter with two 16-bit ADCs with a sampling frequency of 894 kHz and a serial SPI interface that contains all signal processing circuits necessary for measuring the effective voltage and current values , period, active, reactive and apparent power, detecting zero crossing and peak voltage and current values. All received values are stored in the internal registers of the chip. The ADE7753 can work with various types of current sensors, including low resistance shunts and current transformers. In addition, the built-in digital integrator allows you to work with differentiating current sensors such as Rogowski inductors. This direct interface eliminates the need for an analog integrator, ensuring long-term parameter stability and accurate phase matching between voltage and current measurement channels. Depending on the type of current sensor used, the integrator can be connected or disconnected. Based on the data received from the measuring microcircuit, it is possible to calculate the power factor and analyze the energy processes occurring in the network.

The ADE7753 chip is available in a 20-pin SSOP package.

Atmel's popular AT90S2313 AVR microcontroller with 2KB of loading flash memory, 128 bytes of EEPROM and 15 general-purpose I / O lines was chosen as the control microcontroller responsible for all computing operations.

Another important node of the developed digital power factor meter is an indicator for displaying measurement results. The choice fell on the four-line alphanumeric liquid crystal module MT-20S4M of the Russian company MELT, consisting of an LSI control controller and an LCD panel.

Signals proportional to the values of voltage and current in the network are fed through current and voltage sensors to the inputs of the ADE7753 converter chip. After digitization, all further signal transformations, such as multiplication and filtering, occur with the signal in digital form. This approach provides very high stability and accuracy at extreme values of environmental parameters and for a long time.

The microcontroller reads the contents of the internal registers of the ADE7753 chip via the SPI interface and processes the received information to obtain the values of the seven main parameters of electricity. After the microcontroller has completed the processing of data received from the ADE7753 chip, the calculated values are displayed on the liquid crystal display. "

The disadvantages of the analogue are: the lack of analog output signals and the inability to use in automatic control systems, the lack of information about the accuracy of the measurement device in the case of rectangular unipolar current pulses in a single-cycle rectifier circuit.

The source of the prototype (Benin V.L. and Kizilov V.U. Static measuring transducers of electric power. M. "Energy", 1972.) shows the circuit, the principle of operation and analytical conclusions of power converters with sinusoidal reference voltage, using the properties of trigonometric functions ( pg. 47-53).

“In fig. 2a (scanned copy), the transistor T _{1 is} controlled by the difference between the direct current I ₂ and the rectified sinusoidal current , the transistor is open during the time interval when . Transistor T ₁ is a key element of an amplitude modulator powered by a rectified sinusoidal voltage , which is proportional to the current in the measured circuit. In fig. 2 (bd), the curves of the most characteristic voltages and currents in the multiplier-dividing device are shown, provided that the voltages u ₁ and u _{3 are} sinusoidal and phase-shifted by an angle γ. ”

The following is an analytical proof that the average voltage u _H at the resistor r _H (Fig. 2d) is proportional to the active power in the measured circuit.

In fig. 3 (scanned copy) is a schematic diagram of a converter based on a multiplier dividing device shown in Fig. 2.

In the diagram, the primary sensors are a CT current transformer, the load of which is the active resistance r _T , and a VT voltage transformer, from the first secondary winding of which the voltage is rectified by a rectifier V ₂ and filtered by a circuit r ₂ , c ₂ , from the second secondary winding the voltage is supplied to the base of transistors T ₂ , T ₃ to create rectangular pulses in the secondary winding of the TM transformer. The square-wave generator is powered by voltage U ₀ from the voltage regulator CH. The rectangular voltage u _M from the secondary winding of the TM is converted into a sinusoidal reference voltage using a passive low-pass filter L ₁ , L ₂ , C ₁ , which is phase shifted by this filter by approximately 90 °. Fine adjustment of the phase shift by 90 ° is carried out by the circuit r _φ , С _φ , Ζ _φ .

The disadvantages of the prototype are: the impossibility of measuring in electrical circuits with a current shape different from the sinusoidal one, the complexity of the technical implementation of a passive low-pass filter L ₁ , L ₂ , C ₁ , especially in the manufacture of inductors, it is unlikely to obtain a reference sinusoidal voltage with one filter cascade.

The analysis shows that in the device (Fig. 3) there is no amplitude modulation, and there is also no multiplication and division. By multiplication is meant, if you increase the voltage, for example, twice, the current strength also doubles, and the power increases four times, respectively, the duration and amplitude of the pulses increase twice, and the output voltage quadruples - this is impossible called multiplication.

Despite the fact that the prototype is an active power sensor, it can be adopted as a prototype, since the proposed utility model uses a pulse-phase, amplitude converter using the properties of trigonometric functions.

The analysis of the device also shows that by changing the preliminary phase shift by 90 °, you can get a reactive power sensor, and also, under certain conditions, you can get a power factor sensor, so this device is adopted as a prototype.

The technical result is the creation of an analog power factor sensor device with an analog output and the ability to connect a measuring device, the output voltage at cosφ = 1 is at least 5.0 V, high speed (time constant 0.03 s), the ability to measure in electrical circuits of industrial frequency at any form of current, alarm when ahead of the phase shift of the current relative to the voltage.

The technical result is achieved by the fact that in the device of the analog power factor sensor, which contains a pulse-phase, amplitude converter, current transformer and voltage transformer, for any form of current, voltage is supplied from the load resistor of the intermediate current transformer to two low-pass filters in series in the channel current to isolate the voltage of the first harmonic, which is fed to the high-pass filter, after which the voltage is simultaneously applied to the phase-shifting the device and the comparator inverting in the current channel, from the phase shifting device, the voltage is supplied to the comparator not inverting in the current channel, the positive components of the rectangular pulses are allocated from both comparators, which are normalized by logic elements and fed to the inputs of the exclusive OR, the output of which is connected to the inverter on the AND element -NOT, from which short pulses are supplied to the base of a pulse-phase, amplitude converter, an alternating voltage is supplied from a voltage transformer to the input of the comparator does not invert voltage in the channel, from which rectangular polarity pulses are supplied to the integrator, the voltage of which is triangular in shape from which it is supplied to two low-pass filters in series in the voltage channel to obtain a reference sinusoidal voltage, then the voltage is supplied to the phase shifter, from which this voltage is supplied to a precision rectifier, from which voltage is supplied to the collector of a pulse-phase, amplitude converter, the output of which is connected n to a DC filter with an inverting amplifier, then after inverting to the output terminal for connecting the measuring device, in addition, signals from the current and voltage channels are fed to the input of the alarm device.

In the device of the analog sensor of the power factor for any form of current, the first harmonic component is extracted, which serves to produce short pulses of stable duration with the possibility of phase shift when the current phase changes, a reference sinusoidal voltage is generated, which after the rectifier is used as a trigonometric function to determine the power factor , a possible useful signal is used after an exclusive OR with a frequency of 100 Hz.

For this purpose, preliminary experimental studies of the devices for extracting the first harmonic of the current have been conducted. Butterworth low-pass filters with zero bias, bandpass filters with multi-loop feedback and with real poles are investigated. All combinations of their sequential inclusion and variation of the main Q-factors and damping coefficients were also studied. As a result, it was found that the best performance can be obtained with two Butterworth filters in series. However, in this case, increased demands are made on the accuracy of the circuit parameters, otherwise the resulting phase shift between the input and output signals, after inversion, will not be zero. Similar characteristics are obtained with two filters in series with zero offset and damping coefficient ξ = 0.707. Despite the increase in the number of circuit elements, it is advisable to use filters with zero bias, which allows using a variable resistor, with a slight change in the damping coefficient ± 5.0%, to establish after inversion a zero phase shift between the input reference sine wave from the sine wave generator (GSS) and the output of the filters in the current channel at a frequency of 50.0 Hz.

Experimental studies were also conducted to identify the phase shift of the first harmonic at the output of the filters relative to the rectangular pulses at the input, obtained from the reference sinusoid from the GSS. In fig. Figure 4 shows the reference sine wave and rectangular pulses unipolar and bipolar (dashed) obtained using the comparator, which were fed to the input of the filters. In fig. Figure 5 shows the oscillograms of the variable component of the sinusoid at the output of the filters and the rectangular pulses at the input, from which it can be seen that the selected first harmonic has the same phase shift as with the reference sinusoid at the input.

The block diagram of the device of the analog sensor of the power factor is shown in Fig. 6, a schematic diagram in which the elements are dotted and marked in accordance with the structural diagram is shown in Fig. 7.

Circuit Elements:

1 - intermediate current transformer;

2 - the first low-pass filter in the current channel;

3 - the second low-pass filter in the current channel;

4 - high-pass filter;

5 - phase shifting device;

6 - a comparator inverting in the current channel;

7 - the comparator is not inverting in the current channel;

8 - exclusive OR;

9 - inverter on the element AND - NOT;

10 - pulse-phase, amplitude converter;

11 - voltage transformer;

12 - the comparator is not inverting in the voltage channel;

13 - integrator;

14 - the first low-pass filter in the voltage channel;

15 - the second low-pass filter in the voltage channel;

16 - phase shifter;

17 - precision rectifier;

18 - DC filter with an inverting amplifier;

19 - output terminal for connecting the measuring device;

20 is a signaling device.

Brief characteristics of circuit elements:

an intermediate current transformer is connected to a load resistor, on which the voltage is proportional to the current of the measured circuit;

low filters, active on operational amplifiers, second order, with zero bias and with a follower at the output, have an adjustable phase resistor;

high-pass filter of the first order, passing without attenuation the frequency of 50.0 Hz. and not passing a constant component of current;

phase shifting device at (8-10) ° with inverting the sine wave at the output; to normalize the fronts of the pulses after the comparators installed logical elements AND - NOT;

voltage transformer with 6.0 V output;

an integrator on an operational amplifier to obtain a multi-polar voltage of a triangular shape;

phase shifter for adjusting the correspondence of the phases of current and voltage; precision rectifier with positive output voltage;

signal device for lagging or leading the current from voltage in phase.

In the current channel, the primary sensor is an intermediate current transformer 1, the secondary winding of which is connected to the load resistance. The voltage from this resistance U ₁ , proportional to the current, is applied to the input of two series-connected low-pass filters in the second-order current channel 2.3 with zero bias, the output of which is the first harmonic with a constant component U ₂ . The resulting signal is fed to a high-pass filter 4, which passes only the variable component U ₃ . The obtained first harmonic component is supplied simultaneously to two channels. In the first channel, the alternating signal U ₄ is phase shifted by the phase shifting device 5 by (8-10) °, from which it is fed to the input of the comparator inverting current 6 in the channel to convert the sinusoid to rectangular pulses. In the second channel, an alternating signal U ₃ is supplied to the comparator which does not invert current 7 in the channel without phase shift, also to obtain rectangular pulses. Positive pulses are emitted from the outputs of both comparators by diodes, which are normalized by AND elements - NOT U ₅ , U ₆ . The pulses from the AND - elements do NOT arrive at the inputs of the exclusive OR 8, at the output of which U ₇ short pulses (8-10) °, which are then inverted to U _{8 by the} AND - NOT 9 element, from which they are sent to the base of the transistor pulse-phase, amplitude converter 10. Voltage diagrams are shown in Fig. 8 indicating the stresses at the test points.

The primary sensor in the voltage channel is a voltage transformer 11, the alternating voltage from which is converted into rectangular bipolar pulses by a comparator not inverting in the voltage channel 12. From the comparator, the pulses are fed to the input of the integrator 13, the output of which will be a triangular voltage that is better and more accurately converted to a reference sinusoidal voltage using two series-connected low-pass filters in the voltage channel 14, 15. The resulting sinusoidal voltage supplies I at the input of the phase shifter 16 with which the phase can be changed over a wide range variable resistor. Then, the reference voltage is supplied to the input of a precision rectifier 17, from which the voltage in the form of positive half-waves U ₉ is supplied to the collector of a pulse-phase transistor, amplitude converter 10. From the output of which pulses are fed to a DC filter with an inverting amplifier 18, to the output of which U ₁₀ an output terminal can be connected for connecting the measuring instrument 19.

Figure 9 shows the time diagrams of the pulses of the power factor measurement with the indication of the voltages at the control points.

The thus obtained reference voltage in the form of positive half-waves of a sinusoidal shape is used as a trigonometric function from which in the form of short pulses a signal is obtained proportional to the cosine of the angle of shift between voltage and current or power factor.

The rectangular signal from the current measuring channel and the sinusoidal signal from the voltage measuring channel are supplied to the signaling device 20, which gives information about the lag or leading in phase of the current from the voltage. The LED lights when the current lags behind the voltage and does not light when the current is ahead of the voltage.

SCHEME ELEMENTS

Low pass filter

As a low-pass filter, a zero-bias circuit is used (Fig. 10), which has the simplest element settings. The large output impedance R1 is eliminated by the follower DA2.

Transmission function

,

Where - pairing frequency,

2εТ = (С ₁ + C ₂ ) R ₁ ,

- damping coefficient, 2 JRXR2C ^ C2

- quality factor.

, ω ₀ = 2πf = 2π50 = 314c ^-1 .

We define C ₂ > C ₁ and denote , C ₂ = kC ₁

We obtain the calculation formulas for a given ε = 0.707. Initially calculated

, and then

Phase shifter

Phase shifter (Fig. 11) with a gain at any frequency, with R ₂ = R ₃ equal to 1.0.

Gear functions

Phase Equation Equation

φ (ω) = 180-2arctg (ωR ₁ C)

Given C = 0.22 μF, values of R2 = R3 = 10.0 kOhm, for the phase shift φ = 90 °, at ω = ω ₀ , the average value of R _{1 is} calculated, then 2R _{1 is} taken to expand the range of phase control.

High pass filter

High-pass filter fig. 12 is intended to isolate the variable component of the input signal.

Transmission function

,

It is necessary to fulfill the condition

,

so that the signal at the operating frequency f = 50.0 Hz does not decrease in amplitude

Given, for example, C = 1 · 10 ^-6 , we obtain

.

Phase shifting element (Fig. 13)

Transmission function

,

Phase shift

setting φ = -10 °, at ω ₀ = 314 s ^-1 , and setting C = 0.1 · 10 ^-6 f, it is calculated

,

and 1.5 R _{2 is} taken to control φ.

Comparison of the proposed solution not only with the prototype, but also with other technical solutions in this technical field did not allow us to identify signs that match the claimed solution, which allows us to conclude that the utility model has an inventive step. The invention is industrially applicable, it can be used as a sensor for power factor control systems and telemechanization of power supply systems, when measuring temperature in induction plants and in electrical measuring equipment. Thus, the claimed device meets the criteria of the utility model of "novelty."

List of documents cited in the search report

The search was performed in the search engine http://www.fips.ru in the query areas "DEVICE FOR ANALOGUE POWER OUTPUT SENSOR" and "DEVICE FOR POWER OUTPUT MEASUREMENT".

In total, more than 10 abstracts were viewed, as well as open press materials and materials on the Internet. Of these, the most suitable topics were analyzed, the following works:

1. A.Yu. Balzamov A.N. Polivtsev, Single-phase power factor meter. "Mordovian State University named after N.P. Ogareva. " E-mail: mailto: balsamovau@mrsu.ru

2. Benin V.L. and Kizilov V.U. Static measuring transducers of electric power. M. "Energy", 1972

Analysis of devices in the given sources

In [1], a digital measuring device is described, the absence of analog output signals does not allow its use in automatic control systems, and the device does not provide the possibility of operation when measuring when the current is in the form of rectangular unipolar pulses in a single-cycle rectifier circuit.

An active power sensor is given in [2], with the key words: “time is a medium-power pulse converter”, “a transistor is a key element of an amplitude modulator”, “a multiplier-divider device using the properties of trigonometric functions”, which can only work in circuits with sinusoidal forms of current and voltage. Despite the fact that it is an active power sensor, the device can be adopted as a prototype, since in the proposed utility model, as a method, a pulse-phase, amplitude converter using the properties of trigonometric functions is used.

Claims (1)

A device for an analogue power factor sensor, which contains a pulse-phase, amplitude converter, current transformer and voltage transformer, characterized in that for any form of current from the load resistor of the intermediate current transformer, the voltage is supplied to two low-pass filters in series in the current channel to isolate the voltage the first harmonic, which is fed to the high-pass filter, after which the voltage is simultaneously applied to the phase-shifting device and to the compar a torus that inverts in the current channel from a phase shifter, the voltage is applied to a comparator that does not invert in the current channel, positive components of rectangular pulses are extracted from both comparators, which are normalized by logic elements and fed to the inputs of an exclusive OR, the output of which is connected to the inverter on the AND element NOT, from which short pulses are supplied to the base of a pulse-phase, amplitude converter, from a voltage transformer an alternating voltage is supplied to the input of the comparator, not voltage in the channel, from which rectangular polarity impulses are supplied to the integrator, the voltage of which is triangular in shape is applied to two low-pass filters in series in the voltage channel to obtain a reference sinusoidal voltage, then the voltage is supplied to the phase shifter, from which this voltage is supplied to the precision rectifier , from which voltage is supplied to the collector of a pulse-phase, amplitude converter, the output of which is connected to a constant filter eye with an inverting amplifier, then after inversion to the output terminal for connecting the measuring apparatus, furthermore, the signals from the current and voltage are input to the signaling device.