Harmonic Analysis and Control Scheme of Active Filter in Airport Aided Lighting System

Xu Shuang

Ankerui Electric Co., Ltd., Jiading, Shanghai 201801

0 Preface

The airport navigation lighting system is a very important part of the visual navigation aids. It describes the main characteristics of an airport runway, taxiway and approach area through high (medium) light intensity and different color lighting series. Provides a clear visual message for the pilot of the aircraft at night or in poor visibility. The power supply level of the navigation aid lighting system is a particularly important load in the first-order load, and is related to the safe operation of the aircraft. Usually, one or two light substations are installed in the safe area near the runway to provide power for lighting and navigation equipment. Various types of navigation aids are installed on runways and taxiways or on the shoulders. They belong to off-site lamps and have long power supply lines. ICAO recommends the use of series power supply methods. In order to guarantee the power supply in series circuits, there are individual Failure of the lamp does not cause all lamps in the entire circuit to be off, and an isolation transformer must be installed before each lamp. At the same time, the lighting system requires three to five levels of dimming, with the dimmer being dominated by thyristors. Therefore, a large amount of harmonics are generated during the actual operation of the lighting system.

1 Harmonic Harm

With the advancement of science and technology, the development of technology, the application of energy-saving and automated equipment are more and more widely used, and the capacity is also expanding day by day. Although these devices can play a large part of the role of energy saving and consumption reduction, the harmonics generated by them have an effect on the power grid. Pollution, as well as electromagnetic interference, etc., may further affect other electrical equipment in the system and also cause harm.

The definition of the harmonics of the power supply system is: Fourier series decomposition of the periodical alternating current, and the frequency is the component whose integral frequency is greater than one integral multiple of the fundamental frequency. The ratio of the harmonic frequency to the fundamental frequency (n=fn/f1) is called the number of harmonics. Non-integer harmonics sometimes exist in the power grid, called non-harmonics or fractional harmonics. Harmonics are actually a type of interference that causes the grid to become "polluted." Electrical equipment that injects harmonic currents into the utility grid or generates harmonic voltages on the utility grid is called a harmonic source.

Harmonic pollution in the power grid is increasingly serious, causing harm to the power system and various types of electrical equipment. Harmonics will increase the heat loss of electrical equipment. For transformers, for example, the core generates heat loss, especially large eddy current losses. Harmonic currents in the transformer windings induce magnetic flux in the core, resulting in iron losses. Harmonics can also interfere with electronic devices, distorting information, and can cause frequency interference interference in information systems. Harmonic currents flow on high-voltage overhead lines, in addition to increasing line losses, will also have an interference effect on adjacent communication lines. Harmonic wave will increase energy consumption, shorten the life of the equipment, affect the system's operating efficiency, and damage the equipment, resulting in electricity accidents, and even endanger the safe operation of the power system. Therefore, it is very necessary to eliminate the harmonic pollution and control the harmonic content within the allowable range.

2 Harmonic analysis of navigation aid lighting

At present, the harmonic sources in the power system are not only diverse in type, but also widely distributed. The harmonic currents in the user's power grid may come from its own non-linear equipment and may also come from external lines. The electrical equipment with non-linear characteristics is the main harmonic. Wave sources, such as converters with power electronics, AC controllers, transformers, thyristor cascade speed-regulated fan pumps, smelting arc furnaces, etc. If not distinguished, it will cause difficulties for harmonic control.

In the airport navigation lighting system, in order to achieve effective dimming effect, the current world generally uses thyristor constant current dimmer (CCR). The working principle of the constant current dimmer is to use an anti-parallel thyristor regulator to supply power to a step-up transformer. A thyristor conduction angle is determined by a digital regulator to adjust the output current to a reference value. The reference value varies with the selected light level. Under this premise condition, the output current requirement of the constant current dimmer is guaranteed to be a constant value, the first light is 2.8A, the second light is 3.4A, the third light is 4.1A, the fourth light is 5.2A, five Grade light is 6.6A. The constant current dimmer also functions when the load varies from one-half of rated load to full load, maintaining a constant current output in the case of 30% of the isolation transformer secondary open circuit, the change is not greater than plus or minus 2 %. This thyristor regulator and step-up transformer is the main source of harmonics for navigation lights.

Before harmonics treatment, we must understand the number of harmonics in the power grid and its content, that is, the harmonics must be tested. Harmonic measurement is an important part of the harmonic problem, and it is also the main basis for the study of harmonic problems. We performed harmonic detection at the northern light station of the Hongqiao Airport East Runway. The power quality and other data were measured and collected for the low-voltage inlet side of the two transformers at the North Light Station, the runway side light circuit 2, and the dimmer inlet side of the taxiway centerline light circuit 3. (The measurement point is shown in Figure 1)

Figure 1 Measuring point diagram

The specific measurement conditions are as follows:

Measure point 1: The transformer low-voltage side of line B of North Lighting Station, before and after the capacitor cabinet is switched on, real-time measurement of light from level 1 to level 5;

Measure point 2: taxiway center line light circuit 3 dimmer inlet side, real-time measurement of light from level 1 to level 5;

Measured point 3: The low voltage side of the transformer of the North Lighting Station's incoming line A. Before and after the capacitor cabinet is switched, real-time measurement of light from level 1 to level 5 is performed.

Measure point 4: The side of the track side light loop 2 dimmer, real-time measurement of light from level 1 to level 5;

1) Main harmonic source - dimmer (measurement point 1 as an example)

Voltage waveform current waveform

A-phase voltage and current contrast waveform B-phase voltage and current contrast waveform

Phase C voltage and current waveforms Harmonic column distribution

From the comparison of the above figure, it can be seen that the voltage waveform distortion is very small, and the current waveform distortion rate is very serious. This is due to a large number of high-order harmonic superposition resulting in a serious distortion of the sine wave.

From the harmonic columnar graph, it can be seen that the spectrum range of the harmonic current of the thyristor constant current dimmer is very wide. Except for 3, 5, 7, 9, 11 and 13 times, there are also 15, 17, 19, 25, 29 , 31, and 34 higher harmonics. The summary of the data under the condition of the capacitor cabinet removal is shown in Table 1.

Table 1: Summary of Measurement Data (Cut Capacitor Data)

3 governance measures

3.1 Harmonic Treatment Options

From the above system power distribution diagrams and measurement data, it shows that the power quality problems of No. 1 and No. 2 transformer power supply systems at North Light Station are quite prominent. The primary problem is that the harmonic pollution is very serious and the power factor is very low. Because the main load thyristor dimmer under the transformer is a typical nonlinear harmonic source, this device causes a great deal of harmonic pollution in the dimming process, at the same time the current lags behind the voltage seriously, and the power factor is very low; secondly, the adjustment The optical device requires a two-phase power supply (AB phase, BC phase, and CA phase), which will result in severe three-phase imbalance, causing voltage and current fluctuations and a large amount of reactive power in the rapid and frequent switching process of the capacitor cabinet. The impact, while significantly amplifying the system harmonics, further affect the safety and reliability of the power supply and distribution system, there is a hidden danger to the operation of the entire navigation aid lighting system. These issues have also plagued our design and management staff for a long time. Therefore, it is imperative to adopt harmonic control devices to improve the safety and stability of the system, to remove the system harmonics through control, and to increase the power factor and improve the system's three-phase imbalance and other major power quality issues.

Rational design and selection of filters, and proper installation and use of filters, are important steps in suppressing harmonic interference. There are usually several ways:

1) Active Power Filter (APF)

Working principle: The active filter is a power conversion device composed of power electronic components and DSP. After detecting the harmonic current on the load side, it uses the instantaneous extracted reactive components and harmonic components as reference values ​​and actively provides the same. Corresponding reverse compensation current, after the compensation, the rest of the fundamental active current of the system is almost pure sine wave, and its behavior mode is active current source output.

Features: Real-time harmonic currents with equal amplitude and opposite phases cancel the harmonics that need to be dealt with. The harmonics can be dynamically filtered in real time, independent of load changes, and the theoretical filtering rate is greater than 97%.

2) Passive Power Filter (PF)

Working principle: It is composed of LC and other components. It is designed as a very low impedance at a certain frequency, and the harmonic current of the corresponding frequency is shunted. Its behavior mode is to provide some harmonic current bypass; capacitor and reactor are connected in series. Becomes a low-impedance "trap" for the need to govern harmonics.

Features: Only a few harmonics can be filtered and static treatment can be carried out. Under the condition of low load rate, over compensation phenomenon will appear, and resonance with the power grid will easily occur. The theoretical filtering rate is less than 70%.

According to the on-site measurement results, the harmonics of the transformer low-voltage output side of the North Light Station are quite large and the frequency spectrum is very wide. At the same time, the load rate variation range is large and there are some three-phase imbalances. Therefore, it is not suitable to adopt passive filters for control, and there are very few Large resonance risk. The active filter is specially designed for low-voltage power distribution systems with such characteristics. The device has high filtering efficiency, real-time tracking, and fast response. It can effectively filter out load harmonics, suppress system oscillation, and improve the stability of the power grid. At the same time, it has achieved obvious effects of energy saving and power supply equipment expansion.

3.2 Harmonics treatment program Ankerui ANAPF series active power filter is connected to the power grid in parallel to detect the harmonic and reactive components of the load in real time. PWM inverter technology is used to generate a current and current from the converter. The inverse components of harmonic components and reactive components are injected into the power system in real time to achieve harmonic control and reactive power compensation, as shown in Figure 2:

Figure 2 ANAPF active power filter schematic

(1) Centralized governance

It is applicable to occasions where the harmonic content of a single device is small, but the number is large and the layout is scattered, such as office buildings (personal computers, energy-saving lamps, inverter air conditioners, elevators, etc.). Although the current of a single device is small and the harmonic content is low, The entire building has large currents and large harmonic currents, as shown in Figure 3:

Figure 3 centralized management

(2) Local governance

It is applicable to power distribution systems where harmonic sources are concentrated in one or several feeder branches, such as hospital precision instruments and UPS power supplies. Although the current of a single device is small and the harmonic content is low, it is used to prevent other devices from generating power. The harmonics interfere with it and use local harmonic compensation, as shown in Figure 4:

Figure 4 Local Governance

(3) Local governance

It is applicable to distribution systems with clear harmonic sources and large harmonic content in single equipment, such as landscape lighting in large commercial areas, thyristor dimming equipment in theaters, and frequency converters in industrial areas, etc. The device has large current, high harmonic content, and large harmonic current. To prevent harmonic currents from affecting other electrical equipment, local control is used, as shown in Figure 5.

Figure 5 Local governance

3.3 List of major equipment

Active filter quotes and list of major components

4 Conclusion

The dynamic active filter can dynamically filter each harmonic in real time without affecting the load change. It can be installed at the harmonic source, or it can be centralized in substations. The installation is convenient, the energy consumption is small, the efficiency is high, and there is reactive power compensation. And the three-phase balancing function greatly improves the power factor.

After installing the dynamic active filter, all harmonic components of the lighting station are below 3%, which meets the requirements of the total harmonic limit of the public power grid access point (PCC). Each index complies with the "Power Quality Utility Grid Harmony". The National Standard of Waves avoids mutual interference and influence between centralized harmonic source devices, thereby ensuring normal continuous operation of dimmer loads and internal power supply systems. The effect of governance is better, the quality of power supply is improved, and the expected goal of governance is achieved.

references

[1] Ancorui Electric Co., Ltd. Product Manual, 2013.01.

[2] Chai Jieqiong. Analysis and treatment of harmonics in airport navigation lighting system[J]. Electrical Applications, 2013(16)

[3] Civil Airport Flight Area Technical Standard (MH5001-2006)

[4] “Power Quality Harmonics in Public Power Grid” GB/T 14549-93

Xu Shuang, female, undergraduate, Ankerui Electric Co., Ltd., the main research direction for medical power distribution design, mobile phone QQ

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