In urban rail transit vehicles, DC voltages (typically 1500 VDC and 750 VDC) are usually obtained from the grid, and an auxiliary inverter (also called a static inverter) is used to convert the output 380 VAC to supply auxiliary equipment on the train.
Urban rail transit vehicles generally use two types of vehicles. For the two types of vehicles, the inverters work in different forms: the A-type vehicle is a trailer, the inverter supplies the train illumination and the fan Motor all the way, and the other output 110VDC controls the power supply. It also charges the battery; the B/C model is a motor train, and its inverter output 380VAC supplies power to the air conditioning unit and air compressor of the train.
The following is an analysis of the auxiliary circuit system of urban rail transit vehicles.
1 auxiliary inverter circuit structure
There are two common forms of auxiliary inverter circuits in urban rail transit vehicles: one uses direct inverter (DC-AC), as shown in Figure 1; the other uses first-wave (up/down chopper). ) Rear inverter mode (DC - DC - AC), as shown in Figure 2. Siemens uses DC-DC-AC, such as the first, second-line and Guangzhou Line 1 metro vehicles; Bombardier uses DC-AC for vehicles used in Changchun.
Among them DC-DC-AC mode up/step-down chopping, the system of step-up chopper is applied in the case of DC750V power supply network voltage; the system of step-down chopper is applied in the case where the network voltage is DCC500V. The purpose of using the up/down chopping is to stabilize the input voltage of the inverter. When the load changes or the voltage fluctuates, the chopper has a stable output voltage.
At present, the switching frequency of the switching device represented by GTO and IGBT is sufficient to meet the fluctuation range of the network voltage, realize the stable output of the inverter with PWM modulation, and operate at full load. Therefore, the vehicles currently produced often adopt the direct inverter method. .
2 auxiliary inverter form
At present, there are two forms of auxiliary inverters used in urban rail transit vehicles in China: one is a single inverter and the other is a series of two inverters. For example, the Shanghai Metro Line 1 DC subway vehicle uses a single inverter, and the Shanghai Line 2 subway vehicle uses two inverters in series.
2.1 Single inverter form
For an inverter with a network voltage of 1500V and a capacity of about 200kVA, an IGBT component of 3300V / 400A is generally used. This form of structure is simple and reliable, and the PWM modulation of the inverter can make the harmonic content of the output voltage within the limit value, which is a commonly used form.
2.2 Two inverters in series
There are two options: one is to output the two inverters to the isolation transformer, the circuit is superimposed by the isolation transformer, or the magnetic circuit is superimposed, and then filtered output. The advantage of this scheme is that the inverter can use low voltage IGBT components. Second, to control the phase difference between the output voltages of the two inverters, when they are superimposed by the transformer circuit or superimposed on the magnetic circuit, the harmonics of the output voltage of the transformer are reduced, so that the requirements of the output filter can be reduced, that is, can be reduced The size and quality of the small filter.
It should be pointed out that this kind of circuit is more complicated, especially for Transformers, transformers with circuit superposition, and the secondary windings are more complicated. With a magnetic circuit superimposed transformer, the magnetic circuit design is more complicated. On the other hand, the generation of such circuits occurs when the level of early IGBT components is not too high. Therefore, this form has been largely discontinued.
2.3 Auxiliary Power System
Taking the Shanghai Metro Line 1 as an example, the block diagram of the static inverter is shown in Figure 3. The DCl500V power supply is filtered by the GTO chopper to 770V after passing through the LC filter, and then sent to the six-pulse GTO inverter through the intermediate filter. The output is AC380V after the isolation transformer. A set of taps is also arranged on the secondary side of the isolation transformer, and the output AC voltage is rectified to provide DC110V power.
The core of the control unit is the microprocessor, which includes four function packages:
Power Function Pack (P-PAC) - Provides control of power and chopping, inverter pulses.
Communication Function Pack (C-PAC) - Transmits various signals on the inverter and train, and registers the actual values ​​of the process parameters.
Interface Function Pack (I-PAC) - Determines the required values ​​of the parameters, monitors the inverter voltage, current, temperature, delay time and working process.
Fast Protection and Control Function Pack (F-PAC) - Controls the inverter's working process, registers the analog value of the actual value in the process parameters, and achieves fast protection of the inverter.
3 Application and development
On the No. 1 line of Wuhan Light Rail, the auxiliary power supply system uses IGBT module (1700V/1200A) to form a static inverter, and outputs stable three-phase AC380V power supply, DC110V and DC24V power supply for air compressor, air conditioning, lighting and electric heating on the train. It is used by the device and charges the battery. Each train is equipped with two sets of auxiliary power inverters with a capacity of 140KVA.
The auxiliary power supply system of Shanghai Metro Line 2 uses a static inverter consisting of an IGBT module (3300V/1200A) to output AC380V power. Each train of the train is equipped with an auxiliary inverter with a capacity of 90KVA. The inverter of the A car supplies half of the train's lighting and fan motor, and provides DC110V power. The inverters on the B and C cars supply power to half of the air conditioning units of the train.
Metro vehicles mostly use two-shift and one-to-one (three-vehicle vehicles) to form a unit. Two units form a train. Each vehicle is equipped with a static inverter, and each unit shares a DC110V control power supply. The auxiliary inverter of each vehicle has a capacity of 75 ~ 80KVA, and the DC110V control power supply is about 25KW. The subway vehicle produced by ALSTON in France was changed to a unit with 2 static auxiliary inverters, each with a capacity of 120KVA, each containing DC110V control power, with a power of 12KW. Recently, subway vehicles produced abroad have been centrally controlled. In the 6-segment group, each unit is equipped with only one static auxiliary inverter, the capacity is about 250 KVA, and the DC 110V control power supply is about 25KW.
At present, most of the subway and light rail auxiliary systems in the world are composed of insulated gate bipolar transistor IGBT (or IPM) modules. For personal safety, the low-voltage system and the control power supply and the high-voltage system are separated by a transformer at the potential. Nowadays, the scheme of direct-to-straight conversion and high-frequency transformer isolation is adopted at home and abroad. From the perspective of redundancy and axle load balancing, a decentralized power supply scheme is often used.
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