Hydrogen fuel cell hybrid power system based on isolated DC / DC

Abstract

The invention discloses a hydrogen fuel cell hybrid power system based on an isolation DC / DC. The hydrogen fuel cell hybrid power system is characterized by comprising a fuel cell system, a power cell I, an intermediate DC link I, a charging socket, the isolation DC / DC, a power cell II, an intermediate DC link II and an electric transmission system. According to the system, energy conversion and electrical isolation of a fuel cell system and a locomotive electric transmission system are realized by adopting an isolated DC / DC (Direct Current / Direct Current). The problem that rated impulse voltage generated by a main transmission system influences a fuel cell system is solved, and the fuel cell system can meet the voltage requirement of a dielectric strength test of a locomotive electric transmission system. The power battery and the fuel battery system are output in parallel, when the fuel battery system changes the load, the fuel battery can directly obtain energy from the power battery through the non-isolated DC / DC, the power battery is not limited by the isolated DC / DC loading current under the starting and load rising and falling working conditions, and the load increasing and decreasing speed of the fuel battery system is increased.

Description

Technical Field

[0001] The present invention relates to the field of hybrid electric drive systems, and in particular to a hydrogen fuel cell hybrid power system based on isolated DC / DC. Background Art

[0002] At present, the bipolar plate materials of fuel cell stacks are limited by the process, and their operating voltage and insulation level are difficult to further improve. At the same time, the supporting auxiliary components that can meet the durability requirements of fuel cells are all 750V voltage level. Therefore, when designing a hydrogen fuel cell hybrid system, it is necessary to isolate the fuel cell system from the locomotive hybrid system through an isolation DC / DC to meet the vehicle's requirements for dielectric strength tests. Hydrogen energy, as a secondary energy source with abundant sources, green and low carbon, and wide application, is of great significance to the construction of a clean, low-carbon, safe and efficient energy system. In recent years, hydrogen fuel cell technology has continued to develop towards high power, and hydrogen fuel cells are gradually being demonstrated and applied in the field of rail transit. Due to the relatively soft characteristics of fuel cells, they need to be mixed with power batteries to form a hybrid system. At present, there are some matching problems between hydrogen fuel cells and existing locomotive hybrid systems. For example, in the existing technology, hydrogen fuel cell power generation systems, power battery systems, and supercapacitors are connected in parallel to control the locomotive. Therefore, the voltage level of the motor controller and the drive motor needs to be matched according to the output voltage level of the fuel cell. At present, the hydrogen fuel cell system mainly works at a voltage level of 750V, and the intermediate DC link voltage of the locomotive hybrid system can reach up to 900V or even 1500V, which cannot give full play to the traction capacity of the existing locomotive hybrid system. In addition, the hybrid system of fuel cells in the existing technology also has the following defects:

[0003] 1) Insulation coordination between fuel cells and electric drive systems

[0004] Due to the process limitations of the structure and material of the fuel cell stack, the anode and cathode of the stack cannot meet the requirements of rail transit for electrical clearance and creepage distance. According to the insulation resistance requirements in GB 18384-2020, the insulation resistance value of the fuel cell system should meet 100Ω / V or more. The fuel cell stack is connected to the vehicle through a DC / DC converter, which will reduce the insulation of the entire transmission system. Therefore, it is necessary to redesign the DC / DC converter according to the special requirements of rail transit for insulation to meet the requirements of energy conversion and insulation coordination between the fuel cell system and the locomotive electric drive system. Referring to the requirements for insulation resistance test in GB / T25122.1-2018, the insulation resistance of the DC / DC converter should not be less than 1MΩ when the rated insulation voltage does not exceed 1000V, and the insulation resistance ratio should be greater than 1000Ω / V for higher rated insulation voltages. In order to avoid the impact of the rated impulse voltage generated by the main drive system on the fuel cell system, an isolated DC / DC should be used to achieve energy conversion and electrical isolation between the fuel cell system and the locomotive electric drive system.

[0005] 2) Fuel cell loading rate is limited by secondary DC / DC

[0006] The secondary DC / DC needs to switch the working mode when the fuel cell changes load. In the case of startup and load increase, the secondary DC / DC needs to supply the power of the power battery to the fuel cell; in the load reduction condition, the secondary DC / DC needs to switch the mode to output the excess power to the power battery and the bus. If the fuel cell is in the load-pulling condition, when the secondary DC / DC switches from the reverse mode to the forward mode, the large load current will cause the input voltage of the secondary DC / DC to be too high before the mode switching is completed, resulting in the input voltage of the secondary DC / DC to be too high. When the fuel cell is in the load reduction condition, when the secondary DC / DC switches from the forward mode to the reverse mode, if the load reduction current is too large, the secondary DC / DC will not be able to switch in time. At this time, the power demand of the fuel cell will be insufficient, which will cause the fuel cell to report undervoltage and other faults.

[0007] 3) Fuel cell shutdown purge problem

[0008] Since the fuel cell will produce water during operation, some water will remain inside after stopping operation, so the residual water needs to be purged in time before shutting down the fuel cell. At present, during the shutdown process of the fuel cell, the power battery voltage needs to be converted through the secondary DC / DC to power the electrical accessories involved in the purging process. Since the power battery and traction converter are directly connected to the intermediate DC link, once the whole vehicle triggers the electrical protection action, the power battery will be directly cut off, causing the fuel cell protection to shut down, which is likely to cause the fuel cell to produce a hydrogen-oxygen interface and accelerate the aging of the fuel cell.

[0009] 4) Electromagnetic compatibility issues of high-power charging and discharging of power batteries

[0010] The battery management system is an important component of the power battery system. Its main function is to monitor the status of the power battery (temperature, voltage, state of charge, etc.), and can provide communication, safety, cell balancing and management control for the power battery. When charging the power battery, it needs to be connected to the power grid, and the power grid will inevitably carry some byproducts, such as harmonics and indirect lightning. When charging at high power, the electromagnetic environment of the battery management system is relatively complex, which can easily lead to interruption of locomotive charging, and in severe cases, it can even damage the vehicle's charging system. Summary of the invention

[0011] The present invention belongs to the field of hybrid electric drive systems. The fuel cell system is isolated from the hybrid power system by isolating DC / DC, and two groups of power batteries are used. One group of batteries is a power type power battery directly connected to the electric drive system, which can maximize the advantages of high-rate charge and discharge of the power type power battery. One group of batteries uses an energy type power battery with the same voltage level as the fuel cell, which solves the problem that the fuel cell system needs power batteries to provide energy during startup, shutdown, and load change. The present invention mixes fuel cells, energy type power batteries, and power type power batteries by isolating DC / DC. Therefore, the present invention discloses a hydrogen fuel cell hybrid power system based on isolated DC / DC, a fuel cell system, a power battery I, an intermediate DC link I, a charging socket, an isolated DC / DC, a power battery II, an intermediate DC link II, and an electric drive system;

[0012] The power battery I is an energy-type power battery with the same voltage level as the fuel cell, and provides energy for the fuel cell system during startup, shutdown, and load change;

[0013] The power battery II is a power type power battery, connected to the electric drive system, and the fuel cell, energy type power battery and power type power battery are mixed and configured through isolated DC / DC;

[0014] The power battery I is matched with the fuel cell system, the power battery II is matched with the electric drive system, the intermediate DC link I is connected with the intermediate DC link II through an isolated DC / DC, so that the fuel cell system meets the requirements of rail transit insulation coordination. When the locomotive is traction, the fuel cell system, the power battery I and the power battery II are mixed to provide energy to the electric drive system. When the locomotive is electrically braked, the power battery II is used to recover energy first. When the power battery II is full, the power battery I recovers energy through the isolated DC / DC.

[0015] The fuel cell system is connected to the power battery I through a non-isolated DC / DC. Under normal circumstances, the power battery I provides energy for the start-up, shutdown, purge, and load change of the fuel cell system according to different working conditions of the locomotive. When the whole vehicle fails and the power battery II needs to be disconnected, the normal shutdown and purge of the fuel cell system is realized through the power battery I;

[0016] Power battery II provides energy to the electric drive system independently during traction operation. During braking operation, power battery II recovers energy fed back by the electric braking of the locomotive. Under charging operation, power battery I is charged through the charging socket. When power battery I is fully charged, power battery II is charged through the isolated DC / DC.

[0017] The power SOC of the power battery I and the power battery II are detected respectively, and different power SOC control strategies are set: when SOC1≥X2 and SOC2≥Y2, the fuel cell does not work, the power battery I and the power battery II are mixed to provide traction power, and the power battery II is preferentially used to provide energy to the locomotive; when SOC1≥X2 and Y2>SOC2≥Y3, the power battery I is preferentially used to provide energy to the locomotive through the isolated DC / DC.

[0018] When X2>SOC1≥X3, Y2>SOC2≥Y3, the fuel cell starts and provides auxiliary power and traction power to the locomotive first. When the power required by the locomotive is less than the rated power of the fuel cell, the excess power of the fuel cell is used to charge power battery I and power battery II. When the power battery SOC1≥X1, SOC2≥Y1, the fuel cell stops working.

[0019] When X2>SOC1≥X3, Y3>SOC2≥Y4, the fuel cell outputs at rated power and provides power to the locomotive first. When the power required by the locomotive is less than the rated power of the fuel cell, the excess power of the fuel cell is used to charge the power battery II first.

[0020] When X3>SOC1≥X4, Y3>SOC2≥Y4, the fuel cell outputs at rated power and provides power to the locomotive first. When the power required by the locomotive is less than the rated power of the fuel cell, the excess power of the fuel cell is used to charge the power battery I first.

[0021] When SOC1<X4 and SOC2<Y4, the fuel cell system outputs at rated power, charging power battery I first, and power battery II is not allowed to discharge. The locomotive traction auxiliary power is limited to the rated output power range of the fuel cell system.

[0022] Under the locomotive electric braking condition, the generated dynamic braking energy is first used to charge the power battery II, and when SOC2 ≥ X1, the charging of the power battery II is stopped.

[0023] Under the locomotive charging condition, power battery I is charged through the charging socket. When the power battery SOC1≥X1, power battery II is charged through the isolated DC / DC. When SOC2≥Y1, charging stops, among which X1>X2>X3>X4, Y1>Y2>Y3>Y4.

[0024] When the ambient temperature is less than 0°C, the thermal protection system of the power battery I uses the fuel cell cooling system to heat the power battery I. This changes the internal ambient temperature of the power battery and improves the charge and discharge performance of the power battery I.

[0025] Due to the adoption of the above technical solution, the present invention provides a hydrogen fuel cell hybrid power system based on isolated DC / DC, which uses isolated DC / DC to realize energy conversion and electrical isolation between the fuel cell system and the locomotive electric drive system. The impact of the rated impulse voltage generated by the main drive system on the fuel cell system is solved, so that the fuel cell system can meet the voltage requirements of the dielectric strength test of the locomotive electric drive system. The power battery is connected in parallel with the fuel cell system through the non-isolated DC / DC output. When the fuel cell system changes load, the fuel cell can directly obtain energy from the power battery, and is not limited by the isolated DC / DC loading current during startup and load reduction conditions, which improves the load increase and decrease rate of the fuel cell system; the power battery I is directly connected in parallel with the fuel cell. When the whole vehicle triggers the electrical protection action, the power battery I can continue to provide energy for the fuel cell, complete the fuel cell shutdown process, avoid the emergency shutdown of the fuel cell, and greatly improve the reliability and life of the fuel cell system. The power battery II is directly connected to the fuel cell, which can give full play to the advantages of high-rate charging and discharging of power-type power batteries, while also reducing the power of isolated DC / DC charging and discharging, thereby improving the efficiency of the entire transmission system and reducing costs. In addition, the power battery II is charged through the isolated DC / DC on the vehicle to avoid electromagnetic compatibility problems that may arise when the power battery II is directly connected to the power grid. The fuel cell system and the power battery share a cooling system. At low temperatures, the fuel cell cooling system is used to keep the power battery warm, thereby improving the charging and discharging performance of the power battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0027] Figure 1 It is a structural block diagram of the hydrogen fuel cell hybrid power system based on isolated DC / DC of the present invention. DETAILED DESCRIPTION

[0028] In order to make the technical solutions and advantages of the present invention more clear, the technical solutions in the embodiments of the present invention are clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention:

[0029] like Figure 1 A hydrogen fuel cell hybrid power system based on isolated DC / DC is shown, which specifically includes a fuel cell system, a power battery I, an intermediate DC link I, a charging socket, an isolated DC / DC, a power battery II, an intermediate DC link II and an electric drive system. The fuel cell can be mixed with the power battery I and the power battery II to supply power through the converter and the traction motor, or it can provide energy to the traction motor separately according to the hydrogen storage capacity and the SOC value of the power battery.

[0030] The secondary DC / DC is an isolated DC / DC, which can match the output voltage of the hydrogen fuel cell system and power battery I with the intermediate DC link. Power battery I is an energy-type power battery, and power battery II is a power-type power battery. Power battery I provides energy for the start-up, shutdown, purge, and load change of the hydrogen fuel cell system. The fuel cell system and power battery I output a mixed 750VDC direct current, which is increased to 900V or 1500V to match the intermediate DC link through the isolated DC / DC. Power battery II is directly connected to the intermediate DC link, mixed with the isolated DC / DC output, and connected to the converter.

[0031] Furthermore, when the locomotive is operating normally, power battery II is used preferentially to provide energy to the traction inverter and traction motor. During braking conditions, power battery II is used to recover energy fed back by the locomotive's electric brake. Under charging conditions, power battery I is charged through the charging socket. When power battery I is fully charged, power battery II is charged through isolated DC / DC.

[0032] The present invention discloses a control method for a hydrogen fuel cell hybrid power system based on isolated DC / DC, including the following contents:

[0033] Detect the SOC of power battery I and power battery II. When SOC1 ≥ 80% and SOC2 ≥ 70%, the fuel cell does not work, and power battery I and power battery II are mixed to provide traction power, and power battery II is used first to provide energy to the locomotive.

[0034] When SOC1≥80%, 70%>SOC2≥30%, the power battery I is used to provide energy to the locomotive through the isolated DC / DC. When 80%>SOC1≥20%, 70%>SOC2≥30%, the fuel cell starts and provides auxiliary power and traction power to the locomotive first. When the power required by the locomotive is less than the rated power of the fuel cell, the excess power of the fuel cell is used to charge the power battery I and the power battery II. When the power battery SOC1≥90%, SOC2≥90%, the fuel cell stops working;

[0035] When 80%>SOC1≥20% and 30%>SOC2≥10%, the fuel cell outputs at rated power and gives priority to providing power to the locomotive. When the power required by the locomotive is less than the rated power of the fuel cell, the excess power of the fuel cell is used to charge the power battery II first.

[0036] When 20%>SOC1≥10% and 30%>SOC2≥10%, the fuel cell outputs at rated power and gives priority to providing power to the locomotive. When the power required by the locomotive is less than the rated power of the fuel cell, the excess power of the fuel cell is used to charge the power battery I first;

[0037] When SOC1 is less than 10% and SOC2 is less than 10%. The fuel cell system outputs at rated power, and gives priority to charging power battery I. Power battery II is not allowed to discharge, and the locomotive traction auxiliary power is limited to the rated output power range of the hydrogen fuel cell system. When the locomotive is under electric braking conditions, the dynamic braking energy generated is used to charge power battery II. When SOC2 ≥ 90%, energy recovery is stopped;

[0038] Under the locomotive charging condition, power battery I is charged through the charging socket. When the power battery SOC1≥90%, power battery II is charged through the isolated DC / DC, and charging stops when SOC2≥90%. Among them, X1>X2>X3>X4, Y1>Y2>Y3>Y4; X1 takes 90%, X2 takes 80%, X3 takes 20%, and X4 takes 10%. Among them, Y1 takes 90%, Y2 takes 70%, Y3 takes 30%, and Y4 takes 10%.

[0039] When the ambient temperature is less than 0°C, the thermal protection system of the power battery I uses the fuel cell cooling system to heat the power battery I. This changes the internal ambient temperature of the power battery and improves the charge and discharge performance of the power battery I.

[0040] The present invention discloses a hydrogen fuel cell hybrid power system based on isolated DC / DC, which can give full play to the characteristics of three batteries. By using isolated DC / DC to adjust the three batteries under different locomotive working conditions, the reliability of the hydrogen fuel cell system and the efficiency of the entire system are improved.

[0041] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A hydrogen fuel cell hybrid system based on isolated DC / DC, characterized in that include: Fuel cell system, power battery I, intermediate DC link I, charging socket, isolated DC / DC, power battery II, intermediate DC link II and electric drive system; The power battery I is an energy-type power battery with the same voltage level as the fuel cell, and provides energy for the fuel cell system during startup, shutdown, and load change; The power battery II is a power type power battery, connected to the electric drive system, and the fuel cell, energy type power battery and power type power battery are mixed and configured through isolated DC / DC; The power battery I is matched with the fuel cell system, the power battery II is matched with the electric drive system, the intermediate DC link I is connected with the intermediate DC link II through an isolated DC / DC, so that the fuel cell system meets the requirements of rail transit insulation coordination. When the locomotive is traction, the fuel cell system, the power battery I and the power battery II are mixed to provide energy to the electric drive system. When the locomotive is electrically braked, the power battery II is used to recover energy first. When the power battery II is full, the power battery I recovers energy through the isolated DC / DC. The fuel cell system is connected to the power battery I through a non-isolated DC / DC. Under normal circumstances, the power battery I provides energy for the start-up, shutdown, purge, and load change of the fuel cell system according to different working conditions of the locomotive. When the whole vehicle fails and the power battery II needs to be disconnected, the normal shutdown and purge of the fuel cell system is realized through the power battery I; Power battery II provides energy to the electric drive system independently during traction operation. During braking operation, power battery II recovers energy fed back by the electric braking of the locomotive. Under charging operation, power battery I is charged through the charging socket. When power battery I is fully charged, power battery II is charged through the isolated DC / DC.

2. The hydrogen fuel cell hybrid power system based on isolated DC / DC according to claim 1, characterized in that: The power SOC of the power battery I and the power battery II are detected respectively, and different power SOC control strategies are set: when SOC1≥X2 and SOC2≥Y2, the fuel cell does not work, the power battery I and the power battery II are mixed to provide traction power, and the power battery II is preferentially used to provide energy to the locomotive; when SOC1≥X2 and Y2>SOC2≥Y3, the power battery I is preferentially used to provide energy to the locomotive through the isolated DC / DC.

3. A hydrogen fuel cell hybrid power system based on isolated DC / DC according to claim 2, characterized in that: When X2>SOC1≥X3, Y2>SOC2≥Y3, the fuel cell starts and provides auxiliary power and traction power to the locomotive first. When the power required by the locomotive is less than the rated power of the fuel cell, the excess power of the fuel cell is used to charge power battery I and power battery II. When the power battery SOC1≥X1, SOC2≥Y1, the fuel cell stops working.

4. A hydrogen fuel cell hybrid power system based on isolated DC / DC according to claim 3, characterized in that: When X2>SOC1≥X3, Y3>SOC2≥Y4, the fuel cell outputs at rated power and provides power to the locomotive first. When the power required by the locomotive is less than the rated power of the fuel cell, the excess power of the fuel cell is used to charge the power battery II first.

5. The hydrogen fuel cell hybrid power system based on isolated DC / DC according to claim 4, characterized in that: When X3>SOC1≥X4, Y3>SOC2≥Y4, the fuel cell outputs at rated power and provides power to the locomotive first. When the power required by the locomotive is less than the rated power of the fuel cell, the excess power of the fuel cell is used to charge the power battery I first.

6. A hydrogen fuel cell hybrid power system based on isolated DC / DC according to claim 5, characterized in that: When SOC1<X4 and SOC2<Y4, the fuel cell system outputs at rated power, charging power battery I first, and power battery II is not allowed to discharge. The locomotive traction auxiliary power is limited to the rated output power range of the fuel cell system.

7. A hydrogen fuel cell hybrid power system based on isolated DC / DC according to claim 6, characterized in that: Under the locomotive electric braking condition, the generated dynamic braking energy is first used to charge the power battery II, and when SOC2 ≥ X1, the charging of the power battery II is stopped.

8. The hydrogen fuel cell hybrid power system based on isolated DC / DC according to claim 7, characterized in that: Under the locomotive charging condition, power battery I is charged through the charging socket. When the power battery SOC1≥X1, power battery II is charged through the isolated DC / DC. When SOC2≥Y1, charging stops, among which X1>X2>X3>X4, Y1>Y2>Y3>Y4.

9. A hydrogen fuel cell hybrid power system based on isolated DC / DC according to claim 8, characterized in that: When the ambient temperature is less than 0°C, the thermal protection system of the power battery I shares the fuel cell cooling system to heat the power battery I, thereby improving the charge and discharge performance of the power battery I by changing the internal ambient temperature of the power battery.

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