Nov 14, 2020
Localization of AC drive inverter system for urban rail transit
The performance of the AC drive system and the DC drive system are compared , the current situation and development trend of China's urban rail transit are analyzed, and the localization plan of the urban rail transit AC drive inverter system is proposed in combination with the construction of the Beijing Metro Fuba Line.
Keywords: rail transit ; AC drive; inverter; voltage and frequency regulation
1 Comparison of AC drive system and DC drive system
With the development of power electronic devices, control theory and computing technology , AC drives have gradually replaced DC drives, and have shown their advantages in cost performance and operational performance. The first AC drive developed by the BBC company in 1970 Since the advent of the diesel locomotive DE2500, thousands of AC drive locomotives and EMUs have been put into operation. The adhesion coefficient of AC drive locomotives is about 10% higher than that of DC drive locomotives, and the motor type of AC drive locomotives generally adopts simple structure, A squirrel cage asynchronous motor with good reliability, long life and almost maintenance-free.
AC drive locomotives have considerable advantages over DC drives . At present, the railway industry in industrialized countries such as Europe and Japan has basically stopped the production of DC drive electric locomotives. And the chopper-DC motor chopper voltage regulating electric drive system In comparison, the main circuit of the VVVF inverter-AC motor system has become very simple. It is mainly composed of high-speed circuit breakers and less resistance heating. Now, a DC drive electric vehicle with a chopper as the core The group has gradually given way to the AC drive electric vehicle group with VVVF as the core, such as Tokyo in Japan, Seoul in South Korea, Hamburg and Frankfurt in Germany, and Portland in the United States.
2 The status quo and development trend of my country's urban rail transit transmission system
The development of domestic urban rail transit (except Hong Kong) is relatively slow. Except for the subway, there is almost no ground rail transit in urban and suburban areas. At present, only cities such as Beijing, Tianjin, Shanghai and Guangzhou have opened operations.
2.1 Power supply system
The northern area represented by Beijing and Tianjin adopts the DC750V power supply voltage system, and the allowable voltage fluctuation range is DC500V～DC900V, and the third rail receives current ; the southern region represented by Shanghai and Guangzhou adopts the DC1500V power supply voltage system, and the allowable voltage fluctuation range is DC1000V～DC1800V, overhead catenary pantograph receives current .
The above two power supply voltage systems are recommended by the International Electrotechnical Commission, and can meet the power supply requirements of urban rail transit. However, from reducing the power loss and voltage drop of the urban rail transit traction power supply system, extending the power supply distance to reduce the number of traction substations And investment, and in terms of reducing the suspension weight of the current receiving contact network , reducing the structural complexity and investment, the traction power supply voltage system using DC1500V is obviously much more economical than the traction power supply voltage system using DC750V. the development of flow devices, such as the 4500V GTO, 3300V IGBT's, etc., for the use of urban rail transit DC1500V powered traction drive provides a reliable technical art protection . Therefore, the future of China's urban rail transit traction drive system supply voltage standard The development trend should be to gradually adopt a unified DC1500V.
2.2 Traction drive system
Beijing’s subway trains use domestic electric trains , the traction control device is cam resistance and chopper resistance adjustment , and the traction motor is a DC motor. The newly-built Fuba Line (Fuxingmen-Bawangfen) is 16.7km long and is expected to Opened to traffic on October 1, 1999, the traction control device uses a VVVF inverter with GTO components, the traction motor is a squirrel-cage AC motor, and the host is manufactured by Japan's Toyo Electric Company.
Tianjin's subway trains use domestic electric trains , the traction control device is a cam resistor method , and the traction motor is a DC motor. The Shanghai subway trains use German imported electric trains, and the traction control device is a voltage regulator chopper and a traction motor. It is a DC motor. The new line that is being built will also use the AC drive of the VVVF inverter. The Guangzhou Metro train was put into trial operation in June 1997, and all imported EMUs, and the traction control device is a direct-ac VVVF with GTO components. The inverter and traction motor are squirrel-cage AC motors.
It can be seen from the above that the development of the traction drive system of urban rail transit in China in the future will generally adopt the AC drive system of VVVF inverter and squirrel cage asynchronous motor.
3 Localization of AC drive system inverter based on Beijing Metro
The domestically produced AC drive system uses a voltage source VVVF inverter to control a three-phase AC traction motor. The system mainly includes the following equipment: main controller, VVVF inverter system (including inverter main circuit and controller), High-speed circuit breaker box, L2C filter, squirrel-cage asynchronous traction motor, main isolating switch and main fuse, bus isolating switch and high-speed fuse, grounding switch box and grounding device, etc. These devices are in addition to VVVF inverter In addition to the device, the localization of other equipment is relatively easy to achieve, and many devices have been used on Beijing subway trains. Here, the localization plan of VVVF inverters is discussed.
3.1VVVF inverter structure type
The author recommends that the switching device of the AC drive system VVVF inverter should be a commercialized high-power fast switching device IGBT module (if available in the market, an IGBT module with integrated drive and protection circuits can also be used, that is, an IPM module). Commercial high-power IGBT devices currently include: 800A/1700V, 1200A/1700V, 800A/2500V, 1200A/2500V, 800A/3300V, 1200A/3300V, etc. The reason why this solution chooses IGBT instead of GTO is because IGBT Compared with GTO, it has the following advantages: ①Higher switching frequency, improve the quality of inverter output waveform, make noise level and motor loss lower, when the switching frequency of IGBT is 1kHz, electromagnetic noise can be reduced by 3~4dB; ②The gate control is simple , and the trigger energy consumption is low, only 1/20 of GTO; ③The absorption circuit is very simple, and its energy consumption is only 1/60 of the GTO absorption circuit; ④The protection system is simplified, and the protection can be self-shutdown when short-circuited; ⑤High reliability, spare parts can be reduced to 1/10 of the original GTO spare parts; ⑥The weight and size of the same capacity device are greatly reduced.
Of course , no matter whether you choose IGBT or GTO, domestic manufacturers of such large-capacity switching components cannot be produced, and they need to be imported from foreign companies. After the use of IGBT, due to the reduction of component costs, the inverter system is much simplified. Therefore, localization is easier to achieve.
The power supply voltage of China's urban rail transit is DC 750V (allowing 500～900V changes) and DC 1500V (allowing 1000V～1800V changes), so the main circuit structure of VVVF inverter can choose voltage type two-level three-phase inverter structure. For AC drive VVVF inverters powered by DC 750V, the withstand voltage of IGBT devices can be 1700V or 2500V; for AC drive VVVF inverters powered by DC 1500V, the withstand voltage of IGBT devices can be 3300V.
3.2 Control plan
In urban rail transit traction trains , there are two common inverter-motor control schemes for AC drive systems: the first is 1 inverter to control 4 motors; the second is 1 inverter to control 2 motors in response to Beijing Fu - Ba line subway train to say, the rated capacity of one motor is 180kW, it is the first option inverter capacity needs about 1000kVA, the second option takes about 500kVA capacity inverter can be. I recommend the second control scheme, namely one inverter control two motors of the program for the following reasons:. ① urban rail transit vehicles are generally four-axis drive, the second option is the one inverter to control a turn to the frame 2 motors. Compared with the first solution, one inverter controls the 4 motors on the two bogies. The second solution can make full use of the adhesion coefficient between the wheel and the rail, which is more conducive to the traction of the train; ②Using the second scheme, the heat that each inverter needs to remove from the radiator is reduced by half, which makes the heat dissipation treatment easier; ③For the current three-moving, three-to-six-carriage train, if the train If the last inverter fails and is removed for operation, the traction power of the train in the first scheme will be lost 1/3, and the traction power of the train in the second scheme will only be lost 1/6. It can be seen that a second embodiment of the train running ability failure than a first embodiment; ④ conventional IGBT device electrical flow level is 1200A of using the first embodiment requires at least 4 parallel IGBT, the second embodiment uses only two Parallel IGBTs. Two IG2BT parallel current sharing is easier than 4 parallel current sharing .
3.3VVVF inverter control mode
The maximum operating speed of the Beijing subway train is 80km/h, and the average speed is 35-40km/h. Its speed control is realized by the inverter. Detection signals such as the speed of the traction motor, the DC side voltage, and the three-phase output voltage of the inverter It is sent to the control circuit of the inverter, and the inverter controller calculates the voltage and frequency commands according to the operating instructions and the requirements of the motor traction characteristics, and converts them into PWM switching signals to control the switching devices of the inverter, thereby realizing the motor (Electric vehicle unit) speed control. For rail transit traction, the inverter-motor system should meet the following requirements [6-8]: stable typical starting, suppression of coasting and idling, regenerative braking, and wide speed range. to this end, EMU from start to stop transfer speed control modes are as follows :
(1) Constant torque traction control stage. In this stage, the slip frequency (fs) is constant, the voltage/frequency (V/f) is constant, the inverter output frequency gradually increases according to the speed requirements, and the inverter output voltage is PWM Control, can keep the traction force constant, the motor current is basically unchanged. This stage is suitable for motor speed adjustment from zero speed to base speed .
( 2) Constant power traction control stage. The output voltage of the inverter remains unchanged after reaching the maximum value, so that the slip frequency of the motor increases with the frequency of the inverter, and the motor current is maintained unchanged, thereby obtaining constant power control. This stage of the motor The traction force decreases inversely with the increase of the inverter output frequency, which is equivalent to the field weakening control of a DC motor. This stage continues from the base speed of the motor until the slip frequency reaches the given maximum value.
( 3) Traction control stage with natural characteristics. In this stage, the inverter output voltage remains at its maximum value, and the slip frequency remains at its maximum value. The inverter output frequency gradually increases with the speed requirement, and the motor current is proportional to the frequency. The inverse ratio decreases gradually until the maximum operating speed. At this stage, the motor traction decreases inversely proportional to the square of the inverter frequency, which is equivalent to the natural characteristics of a series-excited DC motor under the weakest magnetic field.
( 4) Regenerative braking natural characteristics control stage. This stage is the same as the control mode (3) stage, except that the speed changes from high to low. The motor current increases inversely with the decrease of the inverter output frequency, which should continue to the next stage, but due to the capacity of the inverter, it determines the upper limit of the motor current when the motor current reaches a maximum after the implementation of the constant flow control. in this case the braking torque with reduced inversely proportional to the inverter frequency increases, It is equivalent to the current limit area of DC compound excitation motor.
( 5) Regenerative braking constant torque control stage 1. The inverter voltage still maintains the maximum value. During control, the absolute value of the slip frequency is proportional to the square of the inverter frequency. The inverter frequency follows the speed of the motor. Gradually decrease. At this stage, the motor current basically decreases inversely proportional to the inverter frequency, so that the braking torque remains constant.
( 6) Regenerative braking constant torque control stage 2. This stage is the same as the control mode (1) stage, except that the speed changes from high to low. Regenerative braking constant torque control can continue until the speed drops to 5km/h , Then cut off the electric brake and switch to air brake until it stops.
Main technical indicators of 3.4VVVF inverter system
( 1) The rated voltage of the power supply input voltage is DC750V; the variation range is DC500V～DC900V; the DC side voltage is not higher than 1000V during regenerative braking
( 2) The rated capacity is 2×500kVA; the maximum output capacity is 2×600kVA (when towing).
( 3) Component specifications Switching device IGBT─1700V/1200A, including freewheeling diode.
( 4) Control combination 1 inverter to control 2 180kW squirrel cage motors.
( 5) The inverter controller uses a combination of 16-bit single-chip microcomputer and digital signal processor (DSP). DSP realizes high-speed operation, and 16-bit single-chip microcomputer completes PWM pulses to achieve high-speed and high-precision control of the inverter.
( 6) The output voltage amplitude is 0～550V three-phase AC, the frequency is 1～150Hz, and the three-phase unbalance is the fundamental voltage not exceeding 5%. (7) The efficiency rating is not less than 95%.
( 8) Cooling method The heat pipe exchanges heat energy, and the traveling wind cools naturally.
3.5 Main electrical parameters and performance of traction motors
The type is three-phase 4-pole squirrel-cage asynchronous motor, output power is 180kW (hour system), rated voltage is 550V, rated current is 240A, rated frequency is 77Hz, rated efficiency>92%, rated power factor>0.85, withstand voltage Strength: Press AC3700V (50Hz) for 1min under high temperature conditions, no flashover.
3.6VVVF inverter system protection function
The VVVF inverter is equipped with a monitoring device for fault analysis and maintenance. The inverter system has various protection functions, among which the protection actions caused by minor faults are automatically reset after the system returns to normal or the main controller operation returns to zero.
( 1) Control circuit undervoltage protection When the 110V power supply voltage of the control circuit is lower than 72V, the IGBT pulse is blocked and the main circuit voltage is cut off; when the voltage is higher than 77V, it returns to normal.
( 2) The main circuit under-voltage protection voltage is lower than 450V for 0.2s, cut off the main circuit and block the IGBT pulse; if the voltage is lower than 325V, cut off the main circuit and block the IGBT pulse; when the voltage is higher than 500V, it returns to normal.
( 3) The overvoltage protection voltage of the main circuit is higher than 1050V for 1s, cut off the main circuit, block the IGBT pulse, and open the discharge resistance; if the voltage is higher than 1100V, cut off the main circuit; when the voltage is higher than 900V, it will return to normal.
( 4) Output overcurrent protection When the inverter output current exceeds the set value, the IGBT pulse will be blocked; 0.5s after the overcurrent disappears, it will return to normal. If the overcurrent is still released after the pulse is released, the IGBT pulse will be blocked again and the main circuit will be cut off .
( 5) After the output phase loss protection three-phase detection current is rectified, and the current fluctuation is greater than the set value, the IGBT pulse is blocked and the main circuit is cut off .
( 6) The wheel set idling or coasting protection reduces the motor output current, and implements re-adhesion control according to the predetermined curve.
( 7) Radiator overheat protection When the radiator temperature exceeds 80℃, block the IGBT pulse and cut off the main circuit.
( 8) IGBT short-circuit protection Once the IGBT is short-circuited, follow the short-circuit protection procedure to block the IGBT pulse and it cannot be recovered.
( 9) When the absolute value of the sum of the three-phase current of the current sensor fault protection is greater than the set value, block the IGBT pulse and cut off the main circuit.
4 auxiliary power system
Auxiliary power supply is the power supply for passenger compartment lighting, passenger compartment ventilators, cab air conditioners, battery pack floating charging power supply and system control equipment , and its capacity is 40kW.
The auxiliary power supply uses an IGBT buck-boost DC/DC converter (ie chopper) to convert the grid voltage of DC 500～900V into a stable voltage of DC 750V, and then the IGBT static inverter converts the voltage of DC 750V to The AC voltage of 380V and 50Hz is transformed and rectified by a power frequency transformer to obtain the required voltage. Since IGBT is used as a switching device, there is no need to double the structure of the DC/DC converter, and the AC output does not need to be AC filter.
( 1) The output voltage and capacity of the three-phase AC load is voltage 380×(1±0105), frequency (50±1) Hz, 24kW; DC load one is voltage 110×(1±0101), 15kW; DC load two is Voltage 24×(1±0101)1
( 2) Inverter efficiency>90%1
( 3) The inverter overload capacity is 150% overload, and it will stop automatically after 10s; if it is 200% overload, it will stop immediately 1
( 4) Operating temperature -20℃～+40℃1
( 5) The protection function of the static inverter is the same as that of the VVVF inverter. When the output voltage of the DC/DC converter is greater than 800V, it will shut down for protection.
5 Possibility of localization of inverters for AC drive systems
For the development and commercialization of AC drive VVVF inverters, auxiliary power supply DC/DC converters (ie choppers) and static inverters required by urban rail transit trains , from the current technical level, China is fully capable of Self-reliance is achieved. China's railway system successfully developed the AC4000 AC drive electric locomotive prototype in 1996. Currently, the 200km/h AC drive high-speed EMU is being developed.
The author proposes a localization plan for the AC drive inverter system for rail transit based on the Beijing Metro , and believes that it is appropriate and feasible to use 1700V voltage level IGBTs to form a two-level VVVF inverter for DC 750V AC drive systems. For the auxiliary power supply, China has already successfully applied the 8K electric locomotive, which can be used as a reference for the design of auxiliary power supply for rail transit trains.
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