Analysis and Research on auxiliary inverter power

Analysis and Research on the auxiliary inverter power supply of metro vehicles

Abstract: the circuit structure schemes of the auxiliary inverter power supply of metro vehicles with direct inverter mode, chopper step-down inverter mode and double chopper step-down inverter mode are analyzed. Combined with the technical conditions of imported auxiliary inverter power supply for Beijing "Fuba line" metro vehicles, the development scheme and main technical characteristics of DC750V domestic auxiliary inverter power supply for metro vehicles are introduced. The test waveform of the scheme is given

1 introduction

in recent years, the static auxiliary inverter power supply is used in the auxiliary power supply of metro vehicles introduced by Shanghai, Guangzhou and Beijing. Guangzhou Metro and Shanghai Metro 2# line are IGBT auxiliary inverter power supply; Beijing "Fuba line" is a GTO heat pipe radiator self cooling auxiliary inverter power supply. Therefore, the development and development of static auxiliary inverter power supply for metro vehicles to achieve localization is the inevitable trend of the development of urban rail transit in China. The comparison between the static auxiliary inverter power supply and the traditional power supply mode of electric generator set is as follows:

(1) the static auxiliary inverter power supply receives power directly from the third rail of the metro car, and provides a stable input voltage to the three-phase inverter after dc/DC chopping transformation. Through VVVF frequency and voltage regulation control, the inverter outputs three-phase AC voltage to supply power to the load. For multi-channel output power supply, the circuit adopts the form of transformer isolation. The advantages of this auxiliary inverter power supply are good quality factor of output voltage, high efficiency of power supply and safe and reliable working performance

(2) the traditional auxiliary power supply of subway usually adopts the power supply scheme of rotary electric generator set. The motor receives power from the DC750V third rail, and the generator outputs three-phase AC voltage to supply power to the load. For some DC 110V and DC24V electrical equipment, it still needs to provide power through three-phase transformer and rectifier device. This power supply mode has the advantages of large volume, small output capacity and low efficiency. The power supply is easy to be affected by the changes of working conditions of DC generator units, with large fluctuations in output voltage and poor reliability

2 comparison of auxiliary power supply system schemes for metro vehicles

the following is an analysis and comparison of several commonly used auxiliary inverter circuit structure schemes on DC750V metro vehicles

211 direct inverter mode

Figure 1 is the simplest basic circuit structure of auxiliary inverter power supply for metro vehicles. Switching components can usually adopt high-power GTO, IGBT or IPM. The auxiliary inverter adopts the mode of receiving current directly from the third power rail. The inverter outputs three-phase pulse width modulation voltage to supply power to the load according to the control mode that v/f is equal to a constant. The characteristics of this circuit are simple circuit structure, small number of components used and convenient control, but the disadvantage is that the output voltage of the inverter power supply is easily affected by the fluctuation of the electric input voltage, the input and output are not isolated, the output voltage quality factor is poor, the harmonic content is large, and the load utilization efficiency is low

Figure 1 Schematic diagram of circuit structure of direct inverter auxiliary power supply

212 chopper step-down inverter mode

chopper step-down plus inverter mode auxiliary power supply circuit structure is shown in Figure 2 spring testing machine. This circuit is mainly composed of single tube dc/DC chopper, two-point inverter, three-phase filter, isolation transformer and rectifier circuit. After three-phase filtering, the inverter outputs stable sinusoidal three-phase AC voltage as the power supply for driving three-phase AC loads such as air conditioners and fans. At the same time, the three-phase AC voltage can realize multi-channel DC output of the power supply after transformer and rectification. Its characteristics are as follows

(1) the output voltage of the three-phase inverter is not affected by the fluctuation of the input voltage, and the closed-loop control of dc/DC chopping can keep the input voltage of the inverter constant

(2) each auxiliary inverter chopper only needs one high-power and high-voltage IGBT element, and the inverter can use IGBT elements with lower voltage

(3) since the input voltage of the inverter is constant, for the inverter that only requires CVCF control, only a certain number of ladder wave outputs are required to ensure that the inverter outputs a stable PWM voltage, and the harmonic content is less than 5%

(4) the chopper is distributed on the power supply of each vehicle, and the unit structure is unified. For power supply, although the switching frequency of each power chopper is the same, the chopper phase difference between them is random, which can also realize the multi-phase and multi chopper effect of the chopper

(5) the use of isolation transformer realizes the electrical isolation between electrical input and output loads

Figure 2 Schematic diagram of chopper step-down inverter circuit structure

213 double chopper step-down inverter mode

is basically the same as the auxiliary power circuit of single tube direct dc/DC chopper step-down inverter mode. The double chopper replaces the dc/DC single tube chopper, and the switching components can adopt GTO, IGBT or IPM. The schematic diagram of circuit structure is shown in Figure 3. Its characteristics are as follows

(1) double choppers are used. When the control phases of the upper and lower choppers are staggered by 180 °, the switching frequency of the chopper can be doubled accordingly. Therefore, the volume and weight of the filter device can be greatly reduced, the pulsation of the voltage in the middle DC link of the inverter can be reduced, and the anti-interference ability of the auxiliary inverter power supply can be improved

(2) the closed-loop control of the double chopper plays the role of voltage stabilization and transformation, so it can improve the output efficiency of the inverter

(3) compared with the single tube chopper, the dual dc/DC chopper has twice as many switching components and chopper accessories, but the withstand voltage of the tube can be reduced by half, which improves the service margin of the components and the safety and reliability of the equipment

(4) the transformer isolation between DC power supply and load and the corresponding designed filter can ensure the minimum harmonic of three-phase AC voltage output by the inverter, reduce the impact on the overcharge voltage of the load and improve the service life of the load

Figure 3 Schematic diagram of circuit structure of double chopper step-down inverter mode

214 voltage rise and fall chopper inverter mode

Figure 4 is the schematic diagram of circuit structure of subway auxiliary power supply with voltage rise and fall chopper plus inverter. The front chopper is composed of a smoothing reactor and two switches, diodes and energy storage reactors. The voltage rise and fall chopper is essentially equivalent to two-phase dc/DC converter, and the control system adopts PWM control mode. The constant DC output voltage opposite to the input voltage can be obtained by alternately turning on and off the two switches and appropriately controlling the pulse width according to the output voltage. The latter inverter output is composed of two-point three-phase inverter and three-phase filter. The switching components of chopper and inverter can adopt GTO or IGBT, IPM, etc. The characteristics of this circuit are: the fluctuation of electric voltage does not affect the constant and stable output voltage of the chopper. When the electric voltage is higher than the output voltage of the chopper, the chopper works in the step-down chopper control mode; When the electric voltage is lower than the output voltage of the chopper, the chopper operates in the boost chopper control mode. The alternating on and off of the two switches increases the chopper switching frequency, reduces the volume and capacity of the energy storage reactor and the voltage stress of the switching device, and reduces the pulsation of the output voltage

Figure 4 Schematic diagram of circuit structure of voltage rise and fall chopper inverter mode

3 development and development of auxiliary inverter power supply for subway

as early as the late 1980s, the locomotive and Rolling Stock Research Institute of the Academy of Railway Sciences has begun to adopt advanced converter control technology and new types. 3. Standard configuration problems, high-power GTO and IGBT components, and develop on-board power products. It has successively developed high-power GTO chopper, two image bridge IGBT chopper, on-board IGBT inverter driving high-power linear motor and metro vehicles. In 1999, the air conditioning inverter power supply for DC600V power supply system of passenger cars was developed, and the performance test was passed in Sifang Vehicle Research Institute of the Ministry of Railways in June that year. In September, the vehicle was loaded and operated on the powder preparation, molding and sintering process control technology of k79/80 functional ceramics in Wuchang depot

in 2000, the air conditioning inverter power supply for diesel locomotives and electric locomotives was developed, and the product has been tested in Nanchang internal combustion locomotive depot and Shaowu electric locomotive depot. In 2002, aiming at the technical conditions of imported auxiliary inverter power supply for Beijing "Fuba line" metro vehicles, the locomotive and Rolling Stock Research Institute of the Academy of Railway Sciences developed a DC750V domestic auxiliary power supply engineering unit for metro vehicles, which passed the type test of the locomotive and rolling stock inspection station of the product quality supervision and inspection center of the Ministry of railways. The total capacity of DC750V Metro auxiliary power supply developed is 40 KVA, and the main loads are lighting, ventilator, cab air conditioning unit and vehicle dc110v, DC24V control power supply. Considering the reliability of power supply and the random multiplicity of multi-channel power supply on the vehicle, the main circuit of power supply adopts single tube chopper step-down inverter circuit, high-power IGBT switching elements and heat pipe heat dissipation mode. The double closed-loop PWM control technology of chopper and inverter is adopted to ensure the stability of three-phase AC output voltage and low harmonic content of the power supply. See Table 1 for the main technical parameters. Table 1 main technical parameters of Metro auxiliary power supply device

this Metro auxiliary power supply has the following characteristics

(1) the chopper of the auxiliary power supply adopts the chopper closed-loop control mode to ensure the voltage stability of the DC link in the middle of the inverter when the input voltage changes

(2) the switching frequency of the output inverter is set to 214 kHz, and the harmonic suppression method is adopted, which effectively suppresses the harmonic content of the output voltage and current and the impact on the output high-frequency isolation transformer, and improves the power factor of the inverter and the use efficiency of the load

(3) three phase filter device and isolation transformer are used to realize the electrical isolation between input and output, AC load and DC output power supply

(4) with variable frequency starting mode, the starting current impact of electrical load is small, which is conducive to extending the service life of load equipment

(5) the control system adopts mc80c196 16 bit single chip microcomputer as the main control unit, which has the functions of control, protection, self diagnosis, self recovery, fault storage, LED indicator light and Chinese character display, data transmission, instruction reception and so on

(6) the control system is equipped with short-circuit, overvoltage, undervoltage, overcurrent, overheating, grounding and other fault protection functions, which automatically resume operation after the protection signal disappears, improving the safety and reliability of the subway auxiliary inverter power supply

(7) the main control unit uses a box type plug-in board structure, which is convenient for maintenance, overhaul and replacement of equipment. In order to adapt to the characteristics of high impact and vibration during locomotive operation, the chassis adopts metal frame structure, which has high mechanical strength and good electromagnetic shielding effect

dc750v Metro auxiliary power supply rated load test waveform is shown in Figure 5 ~ figure 8

Figure 5 steady state waveform of input voltage and output voltage Figure 6 output voltage and current waveform

Figure 7 intermediate link voltage start, steady state and stop process figure 8 output voltage, current start, steady state and stop process

conclusion

(1) using static auxiliary inverter power supply to replace the traditional DC generator set power supply device has become an inevitable trend in the development of Metro and light rail transit

(2) the selection of static auxiliary inverter power supply scheme should be combined with the development of domestic power electronics technology, the use level of components and parts, and the development direction of auxiliary inverter power supply for Metro EMUs abroad, and the auxiliary inverter power supply system suitable for Metro and light rail vehicles of urban rail transit in China should be developed

(3) the successful development of Metro static auxiliary inverter power supply marks that we have the ability to develop and produce such domestic experimental machines and have mastered the core manufacturing technology of Metro auxiliary power supply in China