RU2340991C1 - Method of electric energy quality improvement and associated device - Google Patents

Abstract

FIELD: power production.

SUBSTANCE: when non-sinusoidal shape of supply voltage is decreased, electric power is distributed between electronic devices distorting the shape of supply voltage and electronic devices improving the shape of supply voltage during the semi-wave of supply voltage. Device is connected in parallel with consumers introducing distortions of voltage shape. Main voltage is supplied to the device input. Device includes serial connection of phase-shifting chain, control pulse shaper, dc power supply and power switcher, which connects consumers improving the shape of supply voltage to the mains at a certain period of time.

EFFECT: improvement of supply voltage shape and simplification of device design.

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Description

The invention relates to electrical engineering and the electric power industry, and in particular to methods and devices for improving the quality of electric power during the operation of electric consumers, distorting the shape of the network voltage.

In a single-phase network, all consumers are connected in parallel, while the instantaneous current value is determined by the sum of the numerous currents of individual consumers. Among them, we can distinguish consumers that distort the shape of the supply voltage, such consumers have circuits containing rectifier devices with filters. The instantaneous current value of such consumers is a sequence of short alternating pulses following with the frequency of the supply network (Fig. 1, characteristic - 1). The spectrum of current pulses contains a very large number of harmonic components. Reducing the influence of consumers on the form of network voltage is an urgent task.

There is a method of improving the quality of electrical energy, which consists in reducing the level of higher harmonics by tuning several groups of consecutive circuits to a voltage resonance of 5, 7, 11 and 13 harmonics (Zhezhelenko IV "Higher harmonics in power supply systems of industrial enterprises." M: Energoatomizdat, 1984, p. 109). The principle of operation of such devices is based on the appearance of resonance in their own oscillatory circuit tuned to a specific frequency. Filters can be installed in the network to separate linear and nonlinear loads (barrier filters) or to absorb (bypass) currents of higher harmonics.

The main disadvantage of using filters is the incomplete compensation of higher harmonics.

As a prototype, a method has been adopted to improve the quality of electric energy, which consists in extracting higher voltage harmonics from the voltage of the electric network, as well as the first harmonic, determined by the asymmetry voltage, rectifying the selected voltage harmonics, converting the rectified voltage to alternating voltage with a frequency equal to the frequency of the first harmonic of the network, and the return of alternating voltage to the electrical network (patent RU No. 2237334, H02J 3/01, H02J 3/26).

The disadvantage of this method is the incomplete compensation of higher harmonics, limited by the characteristics of the filters included in its composition.

As a prototype of the device adopted an AC voltage stabilizer related to secondary power sources (patent RU No. 2280271 C1, G05F 1/14). The AC voltage stabilizer is designed to reduce the non-sinusoidal form of voltage supplied to an electric consumer with a power consumption of several kilowatts.

The disadvantages of this device are the design complexity, in addition, the digital resistance varies stepwise, which reduces the accuracy of the value of the output characteristic - voltage.

The objective of the proposed method for improving the quality of electricity is to improve the quality of electricity by restoring the shape of the supply voltage to a sinusoidal one by distributing electricity consumption between different consumers.

To implement this task, electricity consumers are divided into groups:

- electronic devices that distort the shape of the supply voltage;

- electronic devices that improve (correct) the shape of the supply voltage.

A way to improve the quality of electricity is based on the distribution of electricity consumption between different consumers during the half-wave.

A way to improve the quality of electrical energy is to reduce the non-sinusoidality of the shape of the supply voltage of the network. The distribution of electricity consumption is made between electronic devices that distort the shape of the supply voltage, and electronic devices that improve the shape of the supply voltage, during the half-wave of the supply voltage.

The method can be implemented using a device for improving the quality of electrical energy containing an output load. At the input of the device, a phase-shifting circuit is installed, connected to the driver of the control pulses, a DC power supply and a power switching key, the outputs of the driver of a control pulse, a DC power source and a power switching key are connected in series.

The method is illustrated by drawings.

Figure 1 shows the shape of the instantaneous current value of various electrical consumers, where 1 - electronic devices that distort the shape of the supply voltage; 2 - electronic devices that improve (correct) the shape of the supply voltage.

Figure 2 shows the connection diagram of device A to improve the quality of electricity, an electronic device B, distorting the shape of the supply voltage, consisting of a diode bridge VD1 ... VD4, a capacitor C1, a resistor R1, and an electronic device C that improves (corrects) the shape of the supply voltage consisting of resistor R2; where u is the network voltage at the point of connection of electric consumers; i ₁ is the instantaneous current value of an electronic device that distorts the shape of the supply voltage; i ₂ - instantaneous current value of an electronic device that improves the shape of the supply voltage; i _sum - the instantaneous value of the total current; Z _ext - internal impedance of the generator; e _generator (t) - EMF generator.

Figure 3 shows a diagram of the proposed device A to improve the quality of electricity, consisting of the following blocks:

1 - phase-shifting chain consisting of a parallel connected capacitor C1 and a resistor R2, to which a resistor R1 is connected in series;

2 - control pulse shaper, consisting of series-connected zener diodes VD1 and VD2, parallel-connected capacitor C2 and resistor R3, to which resistor R4 is connected in series, optotransistors VT1 and VT2 are connected in parallel to resistor R4;

3 - DC power supply, consisting of a step-down transformer T1, the primary winding of which is connected to the mains voltage, a current limiting resistor R5 and a diode bridge VD3 ... VD6 are connected to the secondary winding of the transformer T1, a Zener diode VD7, a capacitor are connected in parallel to the output of the diode bridge C3 and resistor R6;

4 - power switching key, consisting of a diode bridge VD8 ... VD11 and a power transistor VT3 connected in parallel to it;

5 - electronic device that improves the shape of the voltage of the supply network, the resistor R _n .

Figure 4 shows the characteristics of the device for improving the quality of electricity, where

a) the form of voltage;

b) the amount of current supplied to the LEDs of the optotransistors VT1 and VT2, taking into account the phase shift;

c) the magnitude of the control current of the power transistor VT3;

d) the form of voltage on the electronic device C.

It is known that electronic devices consume electricity in a narrow time interval (Fig. 1, characteristic 1) and thereby distort the shape of the supply voltage. To restore the shape of the supply voltage to sinusoidal, it is necessary that another type of load consume electricity in the time interval in which electronic devices that distort the shape of the supply voltage do not consume electricity (Fig. 1, characteristic 2).

When you turn on in parallel with consumers, distorting the shape of the supply voltage, other consumers, the instantaneous value of the total current will be equal to the sum of the instantaneous values of the currents of individual consumers (figure 1, characteristics 1 and 2). Thus, the total value of the instantaneous currents of various consumer groups will reduce the distortion of the shape of the supply voltage.

To implement the proposed method, a device A for improving the quality of electric power is required (Fig. 2), which turns off the electronic device C, which improves the form of the supply voltage (Fig. 2), in the time interval when there is a power consumption by the electronic device B, distorting the form of the supply voltage (figure 2).

The proposed device A to improve the quality of electricity is intended to control the inclusion of a group of electronic devices that improve the shape of the voltage of the supply network at certain points in time (figure 1, characteristic 2)

The voltage of the network is supplied to the input of the device A for improving the quality of electric power (Fig. 3, u) to synchronize the times during which the electronic devices that improve the shape of the voltage are connected to the network and to power the device itself.

To generate control pulses at the required time to open the power switching key, a phase-shifting chain is created consisting of capacitor C1 and resistor R1 (Fig. 3, block 1), which produces a shift of the current shape relative to the shape of the network voltage by an angle close to 90 ° (Fig. .4, b). To create control pulses, two optotransistors VT1 and VT2 are included in the circuit (Fig. 3, block 2). They act as a logical element, which is triggered as a result of excess current through the LED relative to the threshold value. The optotransistor VT1 sets the threshold value i _cpаb1 , VT2 - i _сpаb2 ( _Fig.4 , b). The optotransistors VT1 and VT2 are of the same type, in connection with this the threshold values i _cpаb1 and i _сpаb2 have the same value. When the optotransistor VT1 or VT2 is triggered, the phototransistor located in it opens. Using a DC power source (Fig. 3, block 3) and opening the phototransistor (Fig. 3, block 2, VT1 or VT2), control pulses (Fig. 4, c) are fed to the power switching key. The power switch by means of the power transistor VT3 (figure 3, block 4), in turn, connects to the network at certain points in time electronic devices that improve the shape of the voltage of the supply network. As a result, the voltage supplied to the electronic device C, connected to the network through the device A to improve the quality of electricity, takes the necessary form (figure 4, g or figure 1, characteristic 2). The required duration of the open and closed state of the power transistor VT3 (Fig. 3, block 4) is determined by the selection of the values of the Zener diodes VD1 and VD2 and the capacitor C2 (Fig. 3, block 2).

The advantage of the device for improving the quality of electricity is the simplicity of design, high stability, low power consumption.

To restore the shape of the supply voltage, it is necessary to make the right choice of connection point of the device A to improve the quality of electricity (figure 2). Otherwise, device A for improving the quality of electricity will no longer act as a corrector, but as a source that introduces distortions into the shape of the supply voltage. The device A to improve the quality of electricity should be connected in parallel to consumers B, introducing distortions in the form of the supply voltage (figure 2).

The form of the mains voltage is initially non-sinusoidal due to the fact that the internal resistance of the generator has active and inductive resistance:

where R _generator is the active resistance of the generator; L _generator - generator inductance; i _sum - total current of all consumers; u (t) is the network voltage at the point of connection of electric consumers; e _generator (t) - EMF generator.

соответствовать форме напряжения при холостом ходе генератора.Thus, when using the method of restoring the shape of the supply voltage of the network, it is possible that the shape of the network voltage will be

correspond to the voltage idle form of the generator.

The positive effect is to restore the shape of the supply voltage of the network, bringing it as close as possible to a sinusoidal one. When using the method of improving the quality of electric energy, an economic effect is also observed - reduction of non-production losses of electricity in power supply systems.

Claims (2)

1. A method of improving the quality of electric energy, which consists in reducing the non-sinusoidality of the shape of the supply voltage of the network, characterized in that the distribution of electricity consumption is made between electronic devices that distort the shape of the supply voltage and electronic devices that improve the shape of the supply voltage during half-wave of the supply voltage. 2. A device for improving the quality of electric energy, connected in parallel with consumers, introducing distortions into the voltage form, to the input of which a network voltage is supplied, containing a phase-shifting chain in series, a control pulse shaper, a DC power supply and a power switching key that connects to the network in certain points in time of consumers that improve the shape of the supply voltage.

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