On the relationship between power electronic technology and reactive power compensation and harmonic suppression

Run Junling

(Baotou Power Supply Bureau, Baotou 01400, Inner Mongolia)

Abstract: The article discusses the application and development of power electronics technology in power systems, and analyzes the problems of reactive power and harmonics in power systems

Title, pointed out that power electronics technology is closely related to reactive power compensation and harmonic suppression; and introduced power electronics technology in

The application of power generation, transmission and distribution in the power system finally concluded that with the development of power electronic technology, it can be well

The conclusion to solve its own harmonic and reactive problems.

Keywords: power system; electronic technology; reactive power compensation; harmonic suppression; flexible AC transmission

CLC number: TM714.

It is a kind of power electronic device to transform and control electrical energy

Modern technology enables the power frequency electrical energy of the power grid to be finally converted into electrical energy with different properties and different uses, so as to adapt to the ever-changing electrical equipment

Different needs. Power electronics technology is an emerging edge discipline after the 20th century. Power system is an important leader in the application of power electronics technology

area. The application of power electronics technology in the power system involves improving the transmission capacity, improving the power quality, improving the stability of the power grid operation, and

Reliability, flexibility of control, and loss reduction are major issues. However, power electronics technology has become a

The most important harmonic source in power systems and the harmonic pollution generated by power electronic devices have become a major obstacle to the development of power electronic technology

obstacle. It forces researchers in the field of power electronics to conduct more effective research on harmonic issues to control harmonic pollution and maintain power systems

'Green environment'.

2 Harmonics and reactive power in power systems

2.1 Generation of harmonics and reactive power

Among industrial and domestic electrical loads, resistive load accounts for a large proportion

proportion. Asynchronous motors, transformers, fluorescent lamps, etc. are typical

Inductive load. Resistive load must absorb reactive power to work properly. This is determined by its nature. And the phase-controlled rectifier,

The current on the AC side of power electronic devices such as phase-controlled AC power adjustment circuits and frequency converters often lags the voltage.

It consumes a lot of reactive power and also generates a lot of harmonic currents.

In electrical engineering theory, a pure sinusoidal AC circuit is defined

Three kinds of power: active power P, reactive power Q and apparent power S, they are:

Among them, the phase angle of the current lagging behind the voltage. 3 kinds of power

Meet the relationship:

Active power P represents the product of instantaneous voltage and instantaneous current

The average value of the instantaneous power integrated within a cycle has the physical meaning of AC average power, and the apparent power S represents the maximum of electrical equipment

The usable capacity is the product of the voltage and current effective value as the limit value of the power design of electrical equipment. The rated current is determined by the cross-sectional area of ​​the wire and the copper consumption. The rated voltage is determined by the insulation performance, and

Reactive power means the amplitude of a power interchange in a circuit or system containing an energy storage element. The power interchange in a single-phase circuit occurs directly in electrical

Between the source and the energy storage device (inductor, capacitor), the three-phase circuit is

A load with energy storage characteristics flows back and forth between the three phases. The sum of any instantaneous three-phase reactive power is always equal to zero.

For non-sinusoidal AC circuits, current and voltage can be

Fourier decomposition and expressed in series form, active power and apparent power can still be expressed as:

Among them, Un and In are the fundamental wave and each harmonic voltage and current

Valid value.

Ratio of reactive power in non-sinusoidal circuits containing harmonics

More complicated, so far there is no widely accepted scientific and authoritative definition modeled on pure sinusoidal circuit can define the reactive power of non-sinusoidal circuit

for:

Here, the reactive power (Q) just reflects the flow of energy and

The exchange does not reflect the consumption of energy in the load. In the public power grid, usually the waveform distortion of voltage is very small, while the distortion of current waveform is

It may be very large, so it is very practical to study the situation when the voltage waveform is a sine wave and the current waveform is a non-sine wave without considering the voltage distortion.

Righteousness. Therefore, each power can be expressed as:

Here the reactive power is decomposed into two items, where Qf represents the fundamental wave

The reactive power D generated by the current represents the reactive power generated by the harmonic current. Then the power factor can be expressed as:

In the formula, v = I1 / I is called fundamental factor or waveform distortion factor

Number, cosP1 is the fundamental power factor or displacement factor. visible,

The power factor of a non-sinusoidal current circuit depends not only on the fundamental current phase

The shift is also closely related to the distortion of the current waveform, that is, the size of the harmonic, which is equal to the product of the fundamental wave displacement factor and the waveform distortion factor. So the current

Distortion or harmonics in the circuit will increase the reactive power and reduce the power factor, thereby reducing the availability of the equipment's electrical capacity

This is extremely detrimental to the distribution network where it is located.

22 Impact of reactive power on public power grids

22.1 Increase equipment capacity. The increase in reactive power will cause electricity

The increase in current and the increase in apparent power increase the capacity of the engine, transformers and other electrical equipment and the capacity of the wires.

22.2 Increased equipment and line losses. The increase in reactive power increases the total current and thus increases the loss of equipment and lines.

22.3 Increase the voltage drop of the line and transformer, if it is an impact

The reactive power load will also cause the voltage to fluctuate drastically and seriously reduce the quality of the power supply.

23 Harmonics harm to public power grids and other systems

23.1 Harmonics cause harmonic losses in the components of the public power grid, reducing the efficiency of power generation, transmission and electrical equipment.

When the wave flows through the neutral line, it will overheat the line or even cause a fire.

23.2 Harmonics affect the normal operation of various electrical equipment. harmonic

In addition to causing additional losses, the impact on the motor will also produce mechanical vibration, noise and overvoltage that will cause the transformer to overheat locally;

The cable insulation is aging and the life is shortened to cause damage.

23.3 Harmonics can cause local parallel resonance and

Series resonance, thereby amplifying harmonics

23.4 Harmonics will cause malfunction of relay protection and automatic devices, and will make the measurement of electrical measuring instruments inaccurate.

23.5 Harmonics will cause interference to nearby communication systems

Noise, reduce the quality of communication

The system is not working properly.

3 Harmonic suppression and reactive power compensation

To solve the harmonic pollution of power electronic devices and other harmonic sources

There are two basic ideas for low power factor problems: First, installation compensation

Device to compensate for its harmonics and reactive power;

The device itself is improved so that it does not generate harmonics and does not consume reactive power

Rate or control its power factor as needed.

3.1 Reactive power compensation

In power systems, voltage and frequency measure power quality

The two most basic and important indicators. One of the important methods of voltage control is to control the reactive power of the power system. control

There are many methods of reactive power, including the use of synchronous generators, synchronous power

Motive, synchronous camera, parallel capacitor and static var compensator

It is a typical power electronic device used for reactive power compensation. It uses crystal

The thyratron acts as a solid state switch to control the capacity of the reactor and capacitor connected to the system to change the admittance of the power transmission system. By control object

Different from the control method, it is divided into thyristor control reactor (ThyrisLorControlledReacLor-TCR) and thyristor switching capacitor

Hybrid device (TCR + TSC) TCR and fixed capacitor

(FixedCapaciLor) static reactive power compensation device used in conjunction

MSC) device used in conjunction

Rate, almost 100% capacity capacitors and more than 100% capacity thyristor control reactors consume a lot of copper and iron. From technology

In terms of development, this type of static compensation device cannot be said to be advanced.

In recent years, the development trend is that self-commutated converters composed of turn-off thyristors (GTO) are usually called static reactive power generators

The lagging reactive power can provide advanced reactive power. SVG is divided into two types: voltage type and current type.

The basic structure of the road. Simply put, the basic principle of SVG is to connect the self-commutation bridge circuit through the reactor or directly in parallel to the power grid.

By properly adjusting the phase and amplitude of the output voltage of the AC side of the bridge circuit or directly controlling the AC side current, the circuit can be made

Absorb or emit reactive current that meets the requirements to achieve the goal of dynamic reactive power compensation. Compared with the traditional SVC device represented by TCR

Compared with SVG, the adjustment speed is faster, the operating range is wide and it is adopted.

Measures such as multiplexing, multilevel or PWM technology can greatly reduce the content of harmonics in the compensation current. In addition, the reactor and

Capacitive components are much smaller than those used by SVC, which greatly reduces the size and cost of the device.

a) Use voltage bridge circuit b) Use current bridge circuit

Figure 3 The basic structure of the circuit of the SVG device

3.2 Harmonic suppression

The compensation method uses passive LC filter or active power filter

The wave device belongs to this kind of method. The method of transforming the harmonic source is to try to increase the number of phases of the main harmonic source in the power system, namely the rectifier.

It adopts high power factor rectifier. At present, the most widely used in engineering is the passive LC filter. It has a simple structure, less investment, and high reliability.

Operating costs are also relatively low.

The principle of filtering harmonics is essentially to provide harmonics in the circuit

A release path retains the fundamental wave and short-circuits the harmonics, making the harmonics

Figure 4 Schematic diagram of the filter principle

Power active filters are an important trend in harmonic suppression.

The basic principle is shown in Figure 5. The principle is that the harmonic current is detected from the compensation object. The compensation device generates a harmonic current

Compensating currents that are equal and opposite in polarity so that the grid current contains only the fundamental component. This filter can quickly change the harmonic

The dynamic tracking compensation and the compensation characteristics are not affected by the impedance of the power grid, so it has been widely valued and has been widely applied in Japan and other countries.

use.

Figure 5 Basic principle of power active filter

For power electronics as the main harmonic source

In addition to the use of compensation devices to compensate for its harmonics, there is another way to suppress harmonics is to develop a new converter so that it does not produce harmonics.

Wave and power factor is 1. This kind of converter is called unity power factor converter (UnityPowerFactorconverter).

The electronic device itself does not generate harmonics and reactive power. It is a positive energy-saving and consumption-reducing measure, which can obtain huge economic benefits

In recent years, the research of rate factor converters has become a major issue in the field of power electronics

4 Application of power electronic technology in power system

Power electronics technology is a power semiconductor device, circuit

Technology platform supported by technology, computer technology and modern control technology. After 50 years of development, it has changed equipment in traditional industries

Manufacturing, power quality control, new energy development and civilian products

To more and more widely used. The earliest high-power power electronics technology successfully applied to power systems is direct current transmission (HVDC). from

After the concept of flexible alternating current transmission (FACTS) was put forward in the 1980s, the application research of power electronic technology in power systems has received great attention, and various devices have appeared one after another. In the power system

The power generation link involves a variety of equipment of the generator set, and the application of power electronic technology is to improve the operating characteristics of these equipment as the main purpose. Such as

The static excitation of large generators adopts thyristor rectified self-excitation method, hydraulic power, wind turbine variable speed constant frequency excitation technology and power generation

The frequency conversion speed regulation technology of the factory's fan and water pump uses power electronic technology

In the transmission link, power electronic devices are used in high-voltage transmission systems

They are collectively called the 'second revolution caused by silicon wafers'

Stable operating characteristics of the power grid. DC transmission has the advantages of large transmission capacity, good stability, flexible control and adjustment, etc. For long-distance transmission

Electricity, submarine cable transmission and networking of different frequency systems, high voltage DC

Power transmission has unique advantages. In 1970, the world's first thyristor converter valve pilot project was built in Sweden to replace the original mercury arc

The valve converter marks the formal application of power electronics technology to DC transmission. Since then, all new DC transmission projects in the world

Thyristor converter valve.

The period is a flexible and rapid adjustment of the impedance, voltage and phase of the AC transmission system based on power electronics technology and modern control technology

The power transmission technology can realize the flexible control of the AC power flow and greatly improve the stability of the power system. 20th century 90

Since the 1980s, foreign countries have begun to use FACTS technology in actual power system engineering based on research and development.

The problem that the distribution system urgently needs to solve is how to strengthen the power supply

Reliability and improve power quality. Power quality control not only needs to meet the requirements for voltage, frequency, harmonics and asymmetry but also suppress various

Transient fluctuations and interference. The application of power electronic technology and modern control technology in power distribution system, namely customer power (CustomPower)

Technology or DFACTS technology is a new technology of power quality control developed on the basis of mature technologies of FACTS. can

Understand DFACTS equipment as a reduced version of FACTS equipment

The principle and structure are the same, and the functions are similar. With the power electronic devices

As prices continue to decrease, DFACTS equipment products will enter a period of rapid development.

5 Conclusion

The rapid development of power electronic technology, new materials, new structure devices

Successively born, the advancement of computer technology has provided strong support for the practical application of modern control technology. Some people predict that the power electronics company

Together with motion control, computer technology will become the two most important technologies in the 21st century. Application of power electronic technology in power system

The research is increasingly extensive and in-depth. However, the harmonic and reactive power problems of power electronic devices are a major obstacle to the development of power electronic technology.

Can't avoid it. Fortunately, the use of power electronics technology itself can solve this problem. Power electronics technology will be

The reliability and stability of high power systems play an increasingly important role.

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3 Results and discussion

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When the dosage is 0.6%, the melting resistance is the best, which is the ice cream protection

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"Reference Wennan University

Huang Laifa, Hong Wensheng, Huang Kai, etc. Food thickener.

SB / T10012-92 Determination of the expansion ratio of ice cream "S1.

Liu Meisen, Sheng Mingzhu, He Weiping. The effect of compound emulsifier on the quality of ice cream cake [J1. Cold Drink and Quick Frozen Food Industry,