The use of active power filter device to improve the safety of subway traffic
Along with the continuous development of modern science and technology and the emergence of new technology and new equipment, the number of electrical equipment with nonlinear voltage and current characteristics in the access network is increasing day by day. In the subway system, signal communication, integrated monitoring, automatic fare collection, equipment load UPS DC power and active power filter, traction rectifier units, all kinds of inverter air conditioner, elevators and escalators, energy-saving lamps and other various types of electronic equipment and access to a large number of to the power grid, the non linear load harmonic currents generated by produced in the impedance of the power grid harmonic and power fundamental wave superposition due to distortion. Because of presence of these harmonics due to the instability of electrical railway system in the distribution, will increase the line consumption, affect the automatic control the normal operation of the device and relay protection device, increase the measurement error of the measuring instrument, produce additional heat loss, reduce the safety of the electric equipment, communication signal interference etc.. As is known to all, the electric railway is now undertaking a very important passenger transport task. So harmonic control is very important.
The harm of harmonics to the subway power supply system
1) when the harmonic frequency of the traction system and the natural frequency of the transmission system superposition is likely to enlarge the harmonic component to increase the additional loss of equipment and heating, resulting in equipment failure.
2) for Metro load is near the city center load, harmonics injected into the grid of neighboring the civil power precocious great interference. Also cause interference to the nearby communication system. The most important is to their own harm is very serious, because the subway control center, he sent the information to the outside world can not have the slightest error and delay, no responsibility will cause immeasurable loss. Subway service facilities to provide convenient and fast and safe service, in which personnel intensive occasions there is an elevator failure, power failure, alarm failure will cause confusion and even life safety. So low communication system in Metro must have high quality power to escort. Provide a safe environment for passengers.
3) harmonic reactive power compensation system of produce interference, reduce the power factor and even cause tripping, induced resonance, so that no power compensation capacitor overheating or breakdown, the relay protection device error action affect the power to measuring a series of hazards.
4) station distribution of complex system, the coexistence of strong electricity and weak electricity system, high pressure, low voltage coexist, AC, DC various power supply modes coexist, the harmonic elimination in the source is an important measure to ensure the stable operation of power system.
5) the subway harmonic not only affects the life of electrical equipment, but also shortens the life of electrified railway.
Two, harmonic interference suppression measures
Nearby to absorb harmonic current generated by the harmonic source by active power filter device is effective measure to restrain the harmonic pollution, is currently the distribution system use the most extensive harmonic suppression method. The device is mainly divided into passive filter and active filter.
1) active power filter is the controllable power semiconductor devices to the grid injection with the original harmonic current amplitude is equal and opposite phase current and the power total harmonic current is zero, so as to achieve the purpose of real-time compensation of harmonic current. And passive filter, the biggest difference is that it is a kind of to distribution system injected harmonic current compensation, to counteract nonlinear load harmonic current of active filter device, to change the harmonic of the rapid dynamic tracking compensation and compensation characteristics from the influence of system impedance. The structure is composed of a static power converter, which has high controllability and fast response capability of semiconductor power devices.
Compared with the traditional passive LC filter, the active filter has the following advantages:
A, no resonance phenomenon, the structure of the system, impedance and frequency of change will not affect the compensation effect;
B, the principle than the LC filter better, hired a device will be able to complete the harmonic and fundamental reactive power compensation, also can restrain flicker, 1 machine can characteristics, the price is reasonable.
C, as a high order harmonic current source, is not affected by the system impedance;
D, available in the power factor close to 1, can not be further installed in the case of reactive power devices (passive filter is a capacitive load);
E, even if the frequency of high harmonics can be accurately compensated;
F, the harmonic and fractional harmonics can be effectively suppressed, and the power factor can be improved;
G, because the device itself can complete the output limit, so when the high harmonic quantity is not overload. The main feature of the system is that it can track the harmonic of the frequency and amplitude changes, and the compensation characteristics are not affected by the system impedance. At the same time, the change of reactive power has better expected compensation effect.
2) passive filter installation in the AC side of power electronic devices, by L, C and R components constitute a resonance circuit, when the resonant frequency of the LC circuit and a harmonic current frequency at the same time, you can prevent the harmonics into the power system. Because of the advantages of less investment, high efficiency, simple structure, reliable operation and convenient maintenance, the filter is the main means to restrain harmonics and reactive power compensation.
However, due to the filtering characteristics of the passive filter is determined by the impedance ratio of the power distribution system and the filter device, there are the following disadvantages:
A, it is difficult to coordinate the requirements of filtering, voltage regulation and reactive power compensation;
B, the filter characteristics are greatly influenced by the parameters of the power supply system;
C, can only eliminate a specific number of harmonics, and will have the possibility of some of the harmonic amplification, can not reach the desired filtering effect;
D, cost, volume and so on.
The harm of harmonics to the subway power supply system
1) when the harmonic frequency of the traction system and the natural frequency of the transmission system superposition is likely to enlarge the harmonic component to increase the additional loss of equipment and heating, resulting in equipment failure.
2) for Metro load is near the city center load, harmonics injected into the grid of neighboring the civil power precocious great interference. Also cause interference to the nearby communication system. The most important is to their own harm is very serious, because the subway control center, he sent the information to the outside world can not have the slightest error and delay, no responsibility will cause immeasurable loss. Subway service facilities to provide convenient and fast and safe service, in which personnel intensive occasions there is an elevator failure, power failure, alarm failure will cause confusion and even life safety. So low communication system in Metro must have high quality power to escort. Provide a safe environment for passengers.
3) harmonic reactive power compensation system of produce interference, reduce the power factor and even cause tripping, induced resonance, so that no power compensation capacitor overheating or breakdown, the relay protection device error action affect the power to measuring a series of hazards.
4) station distribution of complex system, the coexistence of strong electricity and weak electricity system, high pressure, low voltage coexist, AC, DC various power supply modes coexist, the harmonic elimination in the source is an important measure to ensure the stable operation of power system.
5) the subway harmonic not only affects the life of electrical equipment, but also shortens the life of electrified railway.
Two, harmonic interference suppression measures
Nearby to absorb harmonic current generated by the harmonic source by active power filter device is effective measure to restrain the harmonic pollution, is currently the distribution system use the most extensive harmonic suppression method. The device is mainly divided into passive filter and active filter.
1) active power filter is the controllable power semiconductor devices to the grid injection with the original harmonic current amplitude is equal and opposite phase current and the power total harmonic current is zero, so as to achieve the purpose of real-time compensation of harmonic current. And passive filter, the biggest difference is that it is a kind of to distribution system injected harmonic current compensation, to counteract nonlinear load harmonic current of active filter device, to change the harmonic of the rapid dynamic tracking compensation and compensation characteristics from the influence of system impedance. The structure is composed of a static power converter, which has high controllability and fast response capability of semiconductor power devices.
Compared with the traditional passive LC filter, the active filter has the following advantages:
A, no resonance phenomenon, the structure of the system, impedance and frequency of change will not affect the compensation effect;
B, the principle than the LC filter better, hired a device will be able to complete the harmonic and fundamental reactive power compensation, also can restrain flicker, 1 machine can characteristics, the price is reasonable.
C, as a high order harmonic current source, is not affected by the system impedance;
D, available in the power factor close to 1, can not be further installed in the case of reactive power devices (passive filter is a capacitive load);
E, even if the frequency of high harmonics can be accurately compensated;
F, the harmonic and fractional harmonics can be effectively suppressed, and the power factor can be improved;
G, because the device itself can complete the output limit, so when the high harmonic quantity is not overload. The main feature of the system is that it can track the harmonic of the frequency and amplitude changes, and the compensation characteristics are not affected by the system impedance. At the same time, the change of reactive power has better expected compensation effect.
2) passive filter installation in the AC side of power electronic devices, by L, C and R components constitute a resonance circuit, when the resonant frequency of the LC circuit and a harmonic current frequency at the same time, you can prevent the harmonics into the power system. Because of the advantages of less investment, high efficiency, simple structure, reliable operation and convenient maintenance, the filter is the main means to restrain harmonics and reactive power compensation.
However, due to the filtering characteristics of the passive filter is determined by the impedance ratio of the power distribution system and the filter device, there are the following disadvantages:
A, it is difficult to coordinate the requirements of filtering, voltage regulation and reactive power compensation;
B, the filter characteristics are greatly influenced by the parameters of the power supply system;
C, can only eliminate a specific number of harmonics, and will have the possibility of some of the harmonic amplification, can not reach the desired filtering effect;
D, cost, volume and so on.
| Datetime：2016.03.29 From： Views：