RU2289876C1 - Method for protecting power consumers against impact of higher-harmonic components - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: proposed method intended to enhance power quality characteristics for users subject to negative influence of higher harmonic components includes generation of circuit current higher harmonic components which are in phase opposition to higher harmonics of supply mains using electrical energy of independent power supply.

EFFECT: enhanced electrical energy quality characteristics for power consumers.

1 cl, 3 dwg

Description

The invention relates to electrical engineering, and in particular to methods providing an increase in the quality parameters of electrical energy for consumers exposed to negative factors of higher harmonic components of electrical energy.

Known methods for reducing the level of higher harmonic components of electrical energy, including power resonant filters, simple notch filters or complex combined filters (band-pass), which serve to filter several harmonics. Power resonant filters of 5, 7, 11 and 13 harmonics are manufactured (Zhezhelenko IV. Higher harmonics in power supply systems of industrial enterprises [Text] / IV Zhezhelenko. - M.: Energoatomizdat, 1984, p. 109). The principle of operation of such installations is based on the occurrence 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. Improving the efficiency of power supply is also provided by the use of power resonant filters as part of high-speed compensating devices. The main disadvantage of the known methods, as shown by their long-term operation, is:

- incomplete compensation of higher harmonics;

- filtering only the highest harmonic components of a certain frequency (number);

- the inability to compensate for higher harmonics with a sharp change in their spectrum.

This leads to increased heating of live parts, triggering of protection of electrical installations, failure of sensitive microprocessor-based process control equipment.

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 electric network (Patent RU No. 2237334 C2, H 02 J 3/01, H 02 J 3/26. A way to improve the quality of electric energy // publ. 2004).

The disadvantage of this method is

- ensuring incomplete compensation of higher harmonics, limited by the characteristics of the filters included in its composition;

- filtering only a certain frequency spectrum of the higher harmonic components;

- the impossibility of satisfactory compensation of higher harmonics with a sharp change in their spectrum.

The invention solves the problem of increasing the quality parameters of electric energy for consumers using power converters and other electrical equipment that are sources of higher harmonics by fully compensating for higher harmonics by generating higher harmonic components of electricity in the network, acting in antiphase with higher harmonics of the main network.

To achieve the named technical result in the proposed method, including the selection of the first and highest harmonics of the current, a higher harmonics generator is used, which represents a controlled thyristor converter, powered by an independent source.

Distinctive features of the proposed method are the generation into the network of higher harmonics of the current of the variable controlled spectrum acting in antiphase with the harmonics of the main network, the use of an independent power source for the generator of higher harmonics, which avoids the allocation of additional higher harmonics of the current to the network from the thyristor converter.

The proposed method is illustrated by the drawings of figure 1 and figure 2, which shows the installation diagram for the compensation of higher harmonics and the current curves at the output of the current transformer and at the input of the analyzer of higher harmonics.

The diagram of Fig. 1 shows a measuring current transformer 1, a higher harmonic analyzer 2 with a first harmonic filter 3, an independent power supply 4, a controlled thyristor converter 5, and a rectifier 6.

The inventive method involves the use of a measuring current transformer 1 (figure 1), which serves to bring the mains current to a value of up to 5 A, which is suitable for further conversion. The current transformer is connected to any of the phases of the electric network due to the symmetry of the higher harmonics in all phases. The requirements of the minimum current and angular errors (accuracy class 0.5) and the absence of distortion of the current conversion at high frequencies (up to 3 kHz) are imposed on the current transformer 1. The current curve at the output 1 is shown in figure 2, a. To analyze the higher harmonic components of the network current, the higher harmonics analyzer 2 (Fig. 1) is used, which is a high-speed analog-to-digital converter connected to current transformer 1 and used to convert information coming from 1 into a digital form suitable for further processing. The analyzer of higher harmonics decomposes the entire spectrum of higher harmonics of the current into frequencies that are multiples of 50 Hz, and determines their level and initial phase. Analyzer 2 is required to operate at a frequency of up to 3 kHz. Given that only the highest harmonic components of the network current are analyzed, it is necessary to exclude the main harmonic curve of the network current from the current curve obtained at the output of transformer 1. For these purposes, the first harmonic filter 3 is used, which represents a resonant filter tuned to the mains frequency (50 Hz) (Fig. 1). Device 3 is connected to input 2 or is included in it. The current curve at the output 3 is shown in figure 2, b. To compensate for higher harmonics, an independent power supply 4 of direct or alternating current is used. To generate higher harmonics of the current in the network, a cascade of high-speed controlled thyristor converters 5 (Fig. 1), which receive power from 4., is used. The controlled thyristor converter represents a device operating on the principle of a frequency inverter. Power 4 and 5 are selected within 1-2% of the rated power of the network. When using an AC power source, it is also necessary to use a power rectifier 6 for power supply 5. The initial phase and the level of higher harmonics of the current generated by 5 are controlled by the feedback principle 2 (Fig. 1), which is carried out by means of an electric network in which compensation. The control criterion is to minimize the level of higher harmonics at a certain frequency. Higher harmonics arising in the network of the power supply supplying the controlled thyristor converter and rectifier do not affect the main network and therefore do not need any compensation.

The structural elements of the installation are subject to the requirements of resistance to high voltage and the safety of personnel at high voltage.

Claims (1)

A method of protecting consumers of electricity from the effects of higher harmonic components, including the separation of the first and highest harmonics of electricity, characterized in that, in order to compensate for higher harmonic components of electricity, generate higher harmonic current components in the network, acting in antiphase with higher harmonics of the main network, using energy independent power source.

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