Rail transit energy storage type traction power supply system and control method thereof

Abstract

The invention discloses a rail transit energy storage type traction power supply system and a control method thereof. The distance between rail transit stations is short, a train is started and braked frequently, regenerated energy can reach more than 40% of traction energy when a locomotive is braked, and meanwhile, the voltage of a traction network is raised. An energy storage system is introduced into an existing traction station of rail transit, the energy storage system comprises a bidirectional DC / DC converter and an energy storage element, and the energy storage element is connected with a traction station direct-current bus through the bidirectional DC / DC converter; the energy storage element adopts a super capacitor; the bidirectional DC / DC converter adopts a topological structure based on half-bridge high-voltage side cascade and low-voltage side multi-phase parallel combination, wherein a bypass resistor is arranged on the high-voltage side of the topological structure. The working state of the energy storage system is controlled by combining different operation conditions of the traction load, and the functions of locomotive regenerative braking energy recycling and traction network voltage fluctuation suppression are achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of recycling and utilizing regenerative energy of rail transit locomotives, and in particular relates to a rail transit energy storage type traction power supply system and a control method thereof. Background Art

[0002] The distance between rail transit stations is short, and trains start and brake frequently. Considering factors such as line slope, curve, vehicle type, station spacing, departure interval, etc., the regenerative energy of the locomotive during braking can reach more than 40% of the traction energy, and at the same time cause the voltage of the traction network to rise. At present, except for a small amount of this energy being absorbed and utilized by adjacent locomotives, most of the remaining energy can be dissipated as heat energy through braking resistors. This method not only wastes regenerative energy, but also increases the cost of ventilation and heat dissipation equipment in the tunnel; on the other hand, it can be fed back to the 35kV AC power grid inside the subway through the inverter feedback device to achieve energy recovery and utilization, but due to the strong impact and volatility of the traction load, it will cause a certain degree of impact on the 35kV AC power grid.

[0003] Regarding the recycling and utilization of renewable energy in rail transit locomotives, the above methods cannot strike a good balance between green environmental protection and economical and stable operation. Energy storage is becoming a trend because it is independent of system operation and has the characteristics of green and high efficiency. Summary of the invention

[0004] In order to make up for the shortcomings of the prior art, the present invention provides a rail transit energy storage traction power supply system and a control method thereof, which controls the working state of the energy storage system in combination with different operating conditions of the traction load, realizes the functions of locomotive regenerative braking energy recovery and traction network voltage fluctuation suppression.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A rail transit energy storage traction power supply system, characterized by:

[0007] An energy storage system is introduced into an existing traction station of rail transit. The energy storage system includes a bidirectional DC / DC converter and an energy storage element. The energy storage element is connected to a DC bus of the traction station via a bidirectional DC / DC converter.

[0008] Furthermore, the energy storage element is a super capacitor.

[0009] Furthermore, the bidirectional DC / DC converter adopts a topological structure based on a half-bridge high-voltage side cascade and a low-voltage side multi-phase parallel combination in which a bypass resistor is set on the high-voltage side.

[0010] Furthermore, it includes two parts: upper layer energy management and lower layer converter control.

[0011] A control method for a rail transit energy storage traction power supply system, the specific steps are as follows:

[0012] Step 1: Take the DC bus voltage U of the traction system dc , the state of charge SOC of the energy storage element is constrained, and the charging voltage and discharging voltage thresholds of the energy storage system are set to be U dc-max , U dc-min ; The maximum charge and minimum discharge state thresholds of the energy storage element are SOC max , SOC min , the working modes of the energy storage system are divided into five types: standby, energy absorption, energy consumption discharge, peak shaving discharge, and forced discharge;

[0013] Step 2: Collect the DC bus voltage U of the traction station dc , DC bus current I dc and the state of charge SOC of the energy storage element;

[0014] Step 3: Based on the principle of system working mode classification, the state value collected in step 2 is compared with the threshold value to determine the current working mode of the energy storage system;

[0015] Step 4: Based on the energy storage system operation mode obtained in step 3, calculate the traction station DC bus power P dc and the energy storage system charging and discharging power rating P ES-充 , P ES-放 , the power reference value P of the energy storage system port in this mode is obtained ES-ref ;

[0016] Step 5: Based on the energy storage system port power reference value P obtained in step 4 ES-ref , the energy storage system port current value i is obtained through the power outer loop ES-ref ;

[0017] Step 6: Based on the energy storage system port current value i obtained in step 5 ES-ref Compared with the actual measured port current value i ES Generate a modulation signal via a current inner loop;

[0018] Step 7: Based on the modulation signal obtained in step 6, a switching signal for controlling the bidirectional DC / DC converter is generated through PWM modulation, and system coordinated control is performed to complete power transfer in each working mode.

[0019] Furthermore, in step 3, the principles for determining the operation mode of the energy storage system are as follows:

[0020] If the DC bus voltage U dc-min dc dc-max ​​, indicating that the traction power supply system is operating in a normal and stable state, and the energy storage system will enter the standby mode; if the DC bus voltage U dc >U dc-max The traction power supply system is running in the regenerative braking state. The regenerative braking energy of the locomotive raises the DC bus voltage. If the energy storage element is charged to the state SOC <SOC max , the energy storage system will enter the energy absorption mode, and the energy storage element will store the regenerated energy of the locomotive. If the energy storage element charge state SOC>SOC max , put the bypass resistor energy-consuming unit into operation to consume the regenerative energy of the feedback regulation and protect the safe operation of the system; if the DC bus voltage U dc dc-min , the traction power supply system operates in the traction energy consumption state, and the locomotive traction consumes energy to lower the DC bus voltage; if the energy storage element charge state SOC>SOC min , the energy storage system will enter the peak-cutting discharge mode, and the energy storage element will release the stored locomotive regenerative energy. If the energy storage element charge state SOC<SOC min , the energy storage system operates in standby mode.

[0021] Furthermore, in step 3, when the energy storage system undergoes major maintenance or is moved, the bypass resistor is used to consume the remaining stored electrical energy.

[0022] Further, in step 4, the reference power value of the energy storage system port in each operation mode is:

[0023] In the standby working mode, the power of the energy storage system port is zero;

[0024] In energy absorption mode, if P dc >P ES-充 , the energy storage system port power is P ES-充 , if P dc <P ES-充 , the energy storage system port power is P dc ;

[0025] In the energy consumption discharge mode, if P dc >P ES-放 , the energy storage system port power is P ES-放 , if P dc <P ES-放 , the energy storage system port power is P dc ;

[0026] In the peak-cutting discharge mode, if P dc >P ES-充 , the energy storage system port power is P ES-充 , if P dc <P ES-充 , the energy storage system port power is P dc ;​

[0027] In the forced discharge mode, the energy storage system port power is P ES-放 .

[0028] Beneficial effects of the present invention:

[0029] 1) The present invention utilizes the energy storage system to recycle the regenerated energy of the locomotive to achieve the purpose of efficient and green energy use;

[0030] 2) The present invention utilizes the "one charge and one discharge" bidirectional operation of the energy storage system to achieve the purpose of suppressing the voltage fluctuation of the traction network;

[0031] 3) The present invention not only improves the utilization rate of locomotive regenerative energy, stabilizes the voltage level of the traction network, but also increases the means of system power regulation, which is of great significance for ensuring efficient, flexible and reliable energy use of the rail transit system. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram of the energy storage type traction power supply system of the present invention;

[0033] Figure 2 The topology diagram of the bidirectional DC / DC converter of the energy storage system of the present invention;

[0034] Figure 3 It is the flow chart of upper energy management module;

[0035] Figure 4 This is the control schematic diagram of the lower converter. DETAILED DESCRIPTION

[0036] The present invention is described in detail below in conjunction with specific implementation modes.

[0037] The present invention utilizes the charging and discharging characteristics of the energy storage system, combines the structure and characteristics of the rail transit traction power supply system, and proposes a rail transit energy storage traction power supply system and a control method thereof; the present invention recycles and utilizes the regenerative braking energy of the locomotive to improve the utilization rate of the regenerative energy; stabilizes the voltage level of the traction network, and increases the system power regulation means.

[0038] like Figure 1 As shown, the present invention introduces an energy storage system into an existing traction station of rail transit, wherein the energy storage system includes a bidirectional DC / DC converter and an energy storage element, and the energy storage element is connected to the DC bus of the traction station via the bidirectional DC / DC converter.

[0039] The energy storage element may be a supercapacitor, a battery, a flywheel or a hybrid component thereof, etc. In this embodiment, a supercapacitor with high power density, fast charge and discharge speed and long service life is used to match the impact and fluctuation of rail transit traction load.

[0040] The bidirectional DC / DC converter can adopt H-bridge cascade, MMC or two-level structures to meet the application requirements of high voltage and high power. In this embodiment, a topological structure based on half-bridge high-voltage side cascade and low-voltage side multi-phase parallel combination with bypass resistors on the high-voltage side is adopted, which is easy to modularize and expand power, while avoiding overcharging of energy storage and increasing system safety and reliability. Figure 2 shown.

[0041] The bidirectional DC / DC converter is composed of two sets of three-phase parallel Buck / Boost converters in cascade. The two sets of devices on the high-voltage side are cascaded to reduce the voltage stress of each switch device to meet the needs of high-voltage applications; the low-voltage side adopts a three-phase parallel Buck / Boost method to reduce the current stress of the switch device and reduce the output current ripple. If a set of three-phase parallel Buck / Boost converters is used as an energy storage unit, it is convenient for modular design; setting a bypass resistor on the high-voltage side can avoid overcharging of energy storage, or discharge when the equipment is powered off for maintenance or moved, thereby increasing the safety and reliability of the system.

[0042] The control method of the rail transit energy storage traction power supply system of the present invention includes two parts: upper layer energy management and lower layer converter control. The specific steps are as follows:

[0043] Step 1: Take the DC bus voltage U of the traction system dc , the state of charge SOC of the energy storage element is constrained, and the charging voltage and discharging voltage thresholds of the energy storage system are set to U dc-max , U dc-min ; The maximum charge and minimum discharge state thresholds of the energy storage element are SOC max , SOC min , the working modes of the energy storage system are divided into five types: standby, energy absorption, energy consumption discharge, peak shaving discharge, and forced discharge;

[0044] Step 2: Collect the DC bus voltage U of the traction station dc , DC bus current I dc and the state of charge SOC of the energy storage element;

[0045] Step 3: Based on the principle of system working mode classification, the state value collected in step 2 is compared with the threshold value to determine the current operating mode of the energy storage system;

[0046] Among them, the principles for judging the operation mode of the energy storage system are as follows: Figure 3 As shown, the brief description is as follows:

[0047] If the DC bus voltage U dc-min dc dc-max ​​, indicating that the traction power supply system is operating in a normal and stable state, and the energy storage system will enter the standby mode; if the DC bus voltage U dc >U dc-max The traction power supply system is running in the regenerative braking state. The regenerative braking energy of the locomotive raises the DC bus voltage. If the energy storage element is charged to the state SOC <SOC max , the energy storage system will enter the energy absorption mode, and the energy storage element will store the regenerated energy of the locomotive. If the energy storage element charge state SOC>SOC max , put the bypass resistor energy-consuming unit into operation to consume the regenerative energy of the feedback regulation and protect the safe operation of the system; if the DC bus voltage U dc dc-min , the traction power supply system operates in the traction energy consumption state, the locomotive traction consumes energy to lower the DC bus voltage, if the energy storage element charge state SOC>SOC min , the energy storage system will enter the peak-cutting discharge mode, and the energy storage element will release the stored locomotive regenerative energy. If the energy storage element charge state SOC<SOC min , the energy storage system operates in standby mode. In addition, when the energy storage system undergoes major maintenance or is moved, bypass resistors are used to consume the remaining stored energy to protect the safety of equipment and personnel.

[0048] Step 4: Based on the energy storage system operation mode obtained in step 3, calculate the traction station DC bus power P dc and the energy storage system charging and discharging power rating P ES-充 , P ES-放 , the power reference value P of the energy storage system port in this mode is obtained ES-ref ;

[0049] Among them, the reference value of the energy storage system port power in each operating mode is:

[0050] In the standby working mode, the power of the energy storage system port is zero;

[0051] In energy absorption mode, if P dc >P ES-充 , the energy storage system port power is P ES-充 , if P dc <P ES-充 , the energy storage system port power is P dc ;

[0052] In the energy consumption discharge mode, if P dc >P ES-放 , the energy storage system port power is P ES-放 , if P dc <P ES-放 , the energy storage system port power is P dc ;

[0053] ​In the peak-cutting discharge mode, if P dc >P ES-充 , the energy storage system port power is P ES-充 , if P dc <P ES-充 , the energy storage system port power is P dc ;

[0054] In the forced discharge mode, the energy storage system port power is P ES-放 ;

[0055] Step 5: Based on the energy storage system port power reference value P obtained in step 4 ES-ref , the energy storage system port current value i is obtained through the power outer loop ES-ref ;

[0056] Step 6: Based on the energy storage system port current value i obtained in step 5 ES-ref Compared with the actual measured port current value i ES Generate a modulation signal via a current inner loop;

[0057] Step 7: Based on the modulation signal obtained in step 6, a switching signal for controlling the bidirectional DC / DC converter is generated through PWM modulation, and system coordinated control is performed to complete power transfer in each working mode.

[0058] In a specific embodiment of the present invention, a simulation model of a rail transit energy storage traction power supply system is constructed, and the working effects under different working modes are analyzed in the order of standby mode, energy absorption mode, energy consumption discharge mode, and peak shaving discharge mode, and each mode lasts for 1 second. Figure 5 The figure shows the simulated waveforms of the inductors and output current of the bidirectional DC / DC converter. Figure 6 The supercapacitor voltage, current and DC bus voltage simulation waveforms. According to the supercapacitor voltage, current and DC bus voltage waveforms, when different working conditions are switched, the DC bus voltage reaches the maximum deviation value after a response speed of about 30ms, and the maximum deviation value is 28V. The corresponding supercapacitor output current does not show obvious overshoot, indicating that the normal operation of the supercapacitor energy storage device will not be affected under this response speed, nor will the current over-limit protection action be triggered. The above simulation results show that the energy storage system can quickly respond to charging and discharging according to the changes in the traction load, has a good inhibitory effect on the voltage fluctuation of the traction network, and has a good dynamic response, thereby verifying the correctness and effectiveness of the rail transit energy storage traction power supply system and its control method.

[0059] The content of the present invention is not limited to the embodiments listed, and any equivalent changes made to the technical solution of the present invention by ordinary technicians in this field after reading the description of the present invention are covered by the claims of the present invention.

Claims

1. A rail transit energy storage traction power supply system, characterized in that: An energy storage system is introduced into an existing traction station of rail transit. The energy storage system includes a bidirectional DC / DC converter and an energy storage element. The energy storage element is connected to a DC bus of the traction station via a bidirectional DC / DC converter.

2. A rail transit energy storage traction power supply system according to claim 1, characterized in that: The energy storage element is a super capacitor.

3. A rail transit energy storage traction power supply system according to claim 2, characterized in that: The bidirectional DC / DC converter adopts a topological structure based on a half-bridge high-voltage side cascade and a low-voltage side multi-phase parallel combination in which a bypass resistor is arranged on the high-voltage side.

4. The control method of a rail transit energy storage traction power supply system according to claim 3 is characterized in that: It includes two parts: upper-level energy management and lower-level converter control.

5. The control method of a rail transit energy storage traction power supply system according to claim 4, characterized in that: The specific steps are as follows: Step 1: Take the DC bus voltage U of the traction system dc , the state of charge SOC of the energy storage element is constrained, and the charging voltage and discharging voltage thresholds of the energy storage system are set to be U dc-max , U dc-min ; The maximum charge and minimum discharge state thresholds of the energy storage element are SOC max , SOC min , the working modes of the energy storage system are divided into five types: standby, energy absorption, energy consumption discharge, peak shaving discharge, and forced discharge; Step 2: Collect the DC bus voltage U of the traction station dc , DC bus current I dc and the state of charge SOC of the energy storage element; Step 3: Based on the principle of system working mode classification, the state value collected in step 2 is compared with the threshold value to determine the current working mode of the energy storage system; Step 4: Based on the energy storage system operation mode obtained in step 3, calculate the traction station DC bus power P dc and the energy storage system charging and discharging power rating P ES-充 , P ES-放 , the power reference value P of the energy storage system port in this mode is obtained ES-ref ; Step 5: Based on the energy storage system port power reference value P obtained in step 4 ES-ref , the energy storage system port current value i is obtained through the power outer loop ES-ref ; Step 6: Based on the energy storage system port current value i obtained in step 5 ES-ref Compared with the actual measured port current value i ES Generate a modulation signal via a current inner loop; Step 7: Based on the modulation signal obtained in step 6, a switching signal for controlling the bidirectional DC / DC converter is generated through PWM modulation, and system coordinated control is performed to complete power transfer in each working mode.

6. The control method of a rail transit energy storage traction power supply system according to claim 5, characterized in that: In step 3, the principles for determining the operating mode of the energy storage system are as follows: If the DC bus voltage U dc-min dc dc-max , indicating that the traction power supply system is operating in a normal and stable state, and the energy storage system will enter the standby mode; if the DC bus voltage U dc >U dc-max , the traction power supply system operates in the regenerative braking state, the locomotive regenerative braking energy raises the DC bus voltage, if the energy storage element charge state SOC <SOC max , the energy storage system will enter the energy absorption mode, and the energy storage element will store the regenerated energy of the locomotive. If the energy storage element charge state SOC>SOC max , put the bypass resistor energy-consuming unit into operation to consume the regenerative energy of the feedback regulation and protect the safe operation of the system; if the DC bus voltage U dc dc-min , the traction power supply system operates in the traction energy consumption state, and the locomotive traction consumes energy to lower the DC bus voltage; if the energy storage element charge state SOC>SOC min , the energy storage system will enter the peak-cutting discharge mode, and the energy storage element will release the stored locomotive regenerative energy. If the energy storage element charge state SOC<SOC min , the energy storage system operates in standby mode.​​​ 7. The control method of a rail transit energy storage traction power supply system according to claim 6, characterized in that: In step 3, when the energy storage system undergoes major maintenance or is moved, the bypass resistor is used to consume the remaining stored electrical energy.

8. The control method of a rail transit energy storage traction power supply system according to claim 7, characterized in that: In step 4, the reference power value of the energy storage system port in each operating mode is: In the standby working mode, the power of the energy storage system port is zero; In energy absorption mode, if P dc >P ES-充 , the energy storage system port power is P ES-充 , if P dc <P ES-充 , the energy storage system port power is P dc ; In the energy consumption discharge mode, if P dc >P ES-放 , the energy storage system port power is P ES-放 , if P dc <P ES-放 , the energy storage system port power is P dc .

9. A control method for a rail transit energy storage traction power supply system according to claim 8, characterized in that: In the peak-cutting discharge mode, if P dc >P ES-充 , the energy storage system port power is P ES-充 , if P dc <P ES-充 , the energy storage system port power is P dc .

10. A control method for a rail transit energy storage traction power supply system according to claim 9, characterized in that: In the forced discharge mode, the energy storage system port power is P ES-放 .

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