Method for starting compressor assembly of fuel cell system
By using the first compressor and turbine running electrically in the compressor assembly of the fuel cell vehicle, combined with speed gradient and bypass control, the problem of rotor jamming is solved, fast and reliable start-up is achieved, components are protected and ensured The stable operation of the system.
Patent Information
- Application Number
- CN202380042167.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2022-05-23
- Filing Date
- 2023-05-10
- Publication Date
- 2025-01-03
AI Technical Summary
Under different operating conditions of fuel cell vehicles, the rotor of the compressor assembly is prone to be stuck due to corrosion or icing, resulting in unstable start and damage to the starting technology, and it is difficult for the prior art to start quickly and reliably.
By introducing an electrically operated first compressor and turbine into the compressor assembly, using different speed gradient values to start and accelerate, check whether the rotor is stuck, and selecting a suitable speed gradient to ensure the rotor free rotation, thereby achieving rapid and reliable and optimize air flow and pressure by controlling turbine bypass and fuel cell bypass.
It realizes the rapid and reliable start of compressor components under different operating conditions, protects gas bearings, avoids excessive wear and damage, and ensures the normal operation of the fuel cell system.
Smart Images
Figure CN119256416A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to a method for starting a compressor assembly of a fuel cell system and to a fuel cell system having a compressor assembly which can be operated by means of the method. Background Art
[0002] In vehicles in which at least a portion of the electrical power required for electric drive is provided by a fuel cell system, a compressor for compressing ambient air and supplying ambient air to the fuel cell system is usually integrated. A large number of different compressor assemblies are known, which are constructed in a single-flow, dual-flow and single-stage or multi-stage manner. Here, a thermal fluid machine is usually used as a compressor. For example, a two-stage compressor assembly includes a first compressor, which has an electric drive. The second compressor connected downstream can be driven via a turbine, which is arranged in the cathode path and in particular in the exhaust path of the fuel cell system. The first compressor and the second compressor and the turbine driving the second compressor are usually supported by air bearings, which require a minimum rotation speed for constructing the corresponding air layer.
[0003] Due to the wide variety of operating conditions of fuel cell vehicles, situations may occur in which, for example, the rotor seizes between the turbine and the second compressor, for example due to corrosion caused by a prolonged standstill of the vehicle or due to ice formation at low ambient temperatures. However, the commissioning of a fuel cell system requires rapid and reliable startup of the compressor assembly taking into account all operating limits in order to prevent damage or excessive wear. Summary of the invention
[0004] The object of the present invention is to specify an alternative method for operating a compressor assembly, by means of which a reliable and rapid start-up of the compressor assembly is possible under different operating conditions and an adaptation to different operating limits is also possible.
[0005] This object is achieved by a method having the features of independent claim 1. Advantageous embodiments and developments of the invention can be gathered from the dependent claims and the following description.
[0006] A method for starting a compressor assembly of a fuel cell system is proposed, the compressor assembly having at least one first compressor that can be operated electrically and a second compressor that is arranged downstream, the second compressor being coupled to a turbine arranged in a cathode path of the fuel cell system via a rotor, the method comprising the following steps: starting the at least one first compressor and accelerating the at least one first compressor to a first rotational speed that corresponds to at least one idling rotational speed of the at least one first compressor, selecting a first rotational speed gradient from a first rotational speed gradient value and a second rotational speed gradient value, wherein the first rotational speed gradient value is greater than the second rotational speed gradient value, accelerating the at least one first compressor from the first rotational speed to the second rotational speed with the first rotational speed gradient, during the acceleration to the second rotational speed, checking whether the rotor rotates freely or whether the rotor is blocked, if the rotor rotates freely, accelerating the at least one first compressor to a maximum starting rotational speed with the aid of the second rotational speed gradient, or maintaining the second rotational speed, repeatedly checking the rotation, and if the rotor rotates freely, accelerating the at least one first compressor to the maximum starting rotational speed, wherein if the probability that the rotor of the turbine is not blocked is greater, the first rotational speed gradient value is selected from environmental parameters and operating parameters of the fuel cell system, and wherein if the probability that the rotor of the turbine is blocked is greater, the second rotational speed gradient value is selected.
[0007] Here, the compressor assembly is a two-stage assembly, wherein the first stage comprises one or more first compressors that can be operated electrically, and the second stage comprises a second compressor that follows downstream. The second compressor is connected to a turbine via a rotor, and the turbine is loaded with exhaust gas from the fuel cell system, in particular. If there is a sufficient exhaust gas flow, the turbine drives the compressor via the rotor if the rotor is not blocked. This can involve single-flow and multi-flow first and / or second compressors.
[0008] The method according to the invention starts with the start of at least one first compressor, which is accelerated, for example, from a standstill to a first rotational speed. If the start of the compressor assembly coincides with a deceleration stop of the compressor assembly after a shutdown that occurred immediately before, the first compressor can also be accelerated from a higher rotational speed than from a standstill to the first rotational speed. The motor of the at least one first compressor can have power electronics, which are designed to bring the gas bearing or air bearing of the at least one first compressor as quickly as possible from the mechanical friction range via the boost speed to a purely aerodynamic operation in order to protect the corresponding components. The idling speed of the at least one first compressor is significantly greater than the boost speed, and the operation of the at least one first compressor can then be carried out permanently, reliably and safely.
[0009] When at least one first compressor is put into operation, the fuel cell system may still be in a shut-down state. The air provided to the cathode path by at least one first compressor enters the exhaust path in the turbine of the fuel cell system leading to the second compressor via the opened cathode bypass path. However, for the reasons mentioned, the rotor may be blocked. In order to take this into account, a first speed gradient is selected in such a way that it is estimated whether the rotor is fixed or freely rotating with a certain probability based on environmental parameters and operating parameters. If the fuel cell system or the compressor assembly has performed a hot start or there is only a short stationary state time of the fuel cell system, the rotor is probably able to rotate freely. In the case of start-stop operation, the same situation may also be the case. On the contrary, if a cold start is performed, or if there is a very long stationary state time, due to the stationary state time, the rotor may be corroded at its bearings, and it can be expected that the rotor is blocked.
[0010] If it is assumed that the rotor is not jammed, the first compressor can be accelerated to the second rotational speed with a greater acceleration. However, in the case where the rotor is approximately stationary, a lower acceleration is achieved. Thus, a possible pumping of the at least one first compressor can be resisted and, moreover, thermal gradients in the compressor assembly can be limited.
[0011] According to the invention, during the acceleration to the second speed, it is checked whether the rotor is rotating. If the rotor is not blocked, the first compressor can then be accelerated to its maximum starting speed, so that the maximum acceleration of the turbine and the second compressor is achieved. The acceleration of the at least one first compressor can be carried out with the largest possible speed gradient. The maximum starting speed mentioned here can correspond to the maximum permissible speed predefined for the at least one first compressor or the maximum speed specified for the start, which is less than the maximum permissible speed.
[0012] Due to the increase in the speed of the at least one first compressor and (as described further below) the position of other elements that influence the flow, a sufficiently high torque is applied to separate the rotor from the static friction of the bearing and then accelerate the rotor as quickly as possible. In addition to achieving good dynamics, the minimum speed of the rotor is also exceeded as quickly as possible, which brings significant advantages to the gas bearing in terms of component protection, because the increase speed is exceeded as quickly as possible.
[0013] If the rotor is detected to be blocked during the check, the rotational speed of the at least one first compressor is limited to a second rotational speed, so that pumping is prevented. In the case of a blocked rotor, the turbine generates additional pressure losses in the cathode path, so that the throttling downstream of the at least one first compressor is greater than in normal operation, and the operating point of the at least one first compressor can be brought closer to the pump characteristic curve. During this time, it can also be checked whether the rotor rotates freely, which may be the case in particular if the rotor is frozen. Staying at the second rotational speed results in a restriction of the operation of the fuel cell system, for example emergency operation.
[0014] As will be explained further below, the first rotational speed gradient value and the second rotational speed gradient value do not necessarily have to be constants in each case, but can also be dependent on other parameters.
[0015] In an advantageous embodiment, the method further comprises: before starting the at least one first compressor or directly after starting the at least one first compressor, closing the turbine bypass. Thus, the greatest possible acceleration of the rotor is achieved, since the entire air mass flow is directed through the turbine and the inlet pressure of the turbine is increased.
[0016] In an advantageous embodiment, the method further comprises: before or directly after starting the at least one first compressor, opening a fuel cell bypass, wherein the fuel cell bypass conducts the compressed intake air in front of the cathode inlet of the fuel cell system into the exhaust path upstream of the turbine. Pressure losses caused by the flow through the fuel cell stack can thus be prevented and the maximum possible pressure is applied to the turbine. In addition, any existing throttle valve can be opened in order to counteract a further pressure reduction.
[0017] In the main embodiment, preferably, the compressor assembly is started while the cathode path of the fuel cell stack is still closed by the shut-off device. In this case, the cathode bypass path needs to be opened.
[0018] In an advantageous embodiment, the second rotational speed gradient value is variable and decreases in the event of a decrease in the ambient temperature or a decrease in the temperature within the compressor assembly, thereby limiting the temperature gradient generated by heating the cathode path by the compressed air.
[0019] In an advantageous embodiment, the second rotational speed is selected such that pumping of the at least one first compressor is prevented in the event of a blocked rotor. The second rotational speed should therefore not be too high in order to prevent pumping if excessive pressure losses occur in the cathode path. However, the second rotational speed should also not be too low in order to enable a blocked rotor to be released. The step of checking cannot be carried out in the event of a rotational speed of the at least one first compressor that is too low, for example less than the idling speed or at around the idling speed, because, for example, a pressure sensor is installed in front of / behind the turbine or in front of / behind the second compressor and a determined pressure level or pressure ratio or pressure difference with respect to the turbine and / or with respect to the second compressor needs to be evaluated, and pressure sensor tolerances need to be taken into account in this regard.
[0020] In an advantageous embodiment, the at least one first compressor is accelerated to the second speed in a plurality of speed steps, which are each held for a predetermined time interval, wherein the check is performed during the time interval. Due to the temporarily fixed operating point, in particular the pressure drop across the turbine and / or the second compressor can be measured more accurately.
[0021] In an advantageous embodiment, the method further comprises: if the rotor has reached at least one minimum rotor speed, a predetermined or predeterminable operating speed is adopted by at least one first compressor, or if the rotor is blocked, the operating restrictions on the fuel cell system are maintained and a predetermined or predeterminable operating speed is adopted when limited to a limited maximum speed. The limited maximum speed is less than the maximum start speed, and in the continued operation, as long as the rotor is blocked, an upper limit is also formed. Thus, the start of the compressor assembly can be ended, and normal operation or limited operation of the fuel cell system can be initiated. Here, the minimum rotor speed takes into account in particular the increase speed for the gas bearing of the turbine or the rotor. If limited operation of the fuel cell system and the compressor assembly is initiated, the steps of checking are continuously repeated until the rotor rotates freely.
[0022] In addition, the present invention relates to a fuel cell system, which has a fuel cell stack, a compressor assembly and a control unit, the compressor assembly having at least one first compressor that can be operated electrically and a second compressor arranged downstream, the second compressor being coupled to a turbine arranged in a cathode path of the fuel cell system via a rotor, the control unit being used to control the fuel cell system, wherein the fuel cell system is configured to implement a method for starting the compressor assembly with the aid of the control unit, the method comprising the following steps: starting at least one first compressor and accelerating at least one first compressor to a first speed corresponding to at least one idling speed of the at least one first compressor, selecting a first speed gradient value from a first speed gradient value and a second speed gradient value A speed gradient, wherein a first speed gradient value is greater than a second speed gradient value, accelerating at least one first compressor from a first speed to a second speed with the first speed gradient, during acceleration to the second speed, checking whether the rotor rotates freely or whether the rotor is blocked, if the rotor rotates freely, accelerating at least one first compressor to a maximum starting speed with the help of the second speed gradient, or maintaining the second speed, repeatedly checking the rotation, and if the rotor rotates freely, accelerating at least one first compressor to the maximum starting speed, wherein if the probability that the rotor of the turbine is not blocked is greater, the first speed gradient value is selected from environmental parameters and operating parameters of the fuel cell system, and wherein if the probability that the rotor of the turbine is blocked is greater, the second speed gradient value is selected.
[0023] In an advantageous embodiment, the fuel cell system furthermore has a turbine bypass, wherein the control unit is designed to close the turbine bypass before or directly after starting the at least one first compressor.
[0024] In an advantageous embodiment, the fuel cell system further comprises a fuel cell bypass, wherein the control unit is designed to open the fuel cell bypass before or directly after starting the at least one first compressor.
[0025] Further measures for improving the invention are shown in more detail below together with the description of preferred exemplary embodiments of the invention with reference to the drawings. BRIEF DESCRIPTION OF THE DRAWINGS
[0026] The accompanying drawings show:
[0027] Figure 1 A fuel cell system is shown.
[0028] Figure 2 A graph is shown with different progressions of the method.
[0029] Figure 3a and 3bTwo diagrams are shown with different speed increases. DETAILED DESCRIPTION
[0030] Figure 1 A fuel cell system 2 is shown, which is controlled via a control unit 3. The fuel cell system 2 has a compressor assembly 4, which comprises a first compressor unit 6, an electric motor 10 and an inverter 12, the first compressor unit having two first compressors 8. The two first compressors 8 are connected to the motor 10 via a shaft 14, and the operating voltage is supplied to the motor via the inverter 12. The inverter 12 can be controlled from the outside in order to set the speed of the motor as required.
[0031] In addition, the compressor assembly 4 has a second compressor unit 16 and a turbine 20, wherein the second compressor unit has a second compressor 18, and the second compressor unit and the turbine are coupled to each other via a rotor 22. The second compressor 16 is located downstream of the first compressor 8 and provides compressed air to the intake path 24 of the fuel cell stack 26. The exhaust gas from the fuel cell stack 26 flows into the exhaust path 28 and enters the turbine 20 from there. Next, the exhaust gas can flow out to the environment 30 downstream of the turbine 20. The intake path 24 and the exhaust path 28 can be combined into a cathode path. In addition, an intercooler 32 is provided downstream of the second compressor 18, which cools the compressed intake air before entering the fuel cell stack 26. There is a first shut-off valve 34 downstream of the intercooler 32, which prohibits the intake air flow into the fuel cell stack 26 as required. There is a second shut-off valve 36 downstream of the fuel cell stack 26, which is used to interrupt the connection of the fuel cell stack 26 with the exhaust path 28 as required. The fuel cell stack 26 can be bypassed via a fuel cell bypass 38. The fuel cell bypass 38 has a fuel cell bypass valve 40, which can be opened and closed as needed. A further heat exchanger 42 can be provided between the fuel cell stack 26 and the second compressor unit 16, which transfers heat from the intake path 24 to the exhaust path 28. In addition, an additional intercooler 44 can be arranged between the first compressor unit 6 and the second compressor unit 16, which cools the air flowing into the second compressor 18. An air filter 46 is arranged in front of the first compressor unit 6, which filters the air from the environment 30 and supplies it to the first compressor unit 6. The turbine 20 can be bypassed by the turbine bypass 48. The turbine bypass 48 has a turbine bypass valve 50, which can be opened and closed as needed. In addition, an exhaust shut-off valve 52 is also provided downstream of the turbine 20.
[0032] The fuel cell system 2 can execute a method for starting the compressor assembly 4 in a manner controlled by the control unit 3. Here, the first compressor 8 is started and accelerated to a first speed, which corresponds to at least one idling speed of the first compressor 8. A first speed gradient is selected from a first speed gradient value and a second speed gradient value, wherein the first speed gradient value is greater than the second speed gradient value. As described above, the speed gradient value is selected based on an evaluation of environmental parameters and operating parameters of the fuel cell system 2. If the probability that the rotor 22 of the turbine 20 is not blocked is greater, the first speed gradient value is selected. If the probability that the rotor 22 of the turbine 20 is blocked is greater, the second speed gradient value is selected.
[0033] The first compressor 8 is accelerated from the first speed to the second speed with a first speed gradient. During the acceleration to the second speed, it is checked whether the rotor 22 rotates freely or whether the rotor is blocked. If the rotor rotates freely, the first compressor 8 is then accelerated to the maximum starting speed with the second speed gradient, or if the rotor 22 is blocked, the second speed is maintained, wherein the rotation of the rotor 22 is repeatedly checked. If the repeated checks show that the rotor 22 rotates freely, the first compressor 8 is accelerated to the maximum starting speed.
[0034] During startup, the fuel cell bypass 38 may be open and the turbine bypass 48 may remain closed. If necessary, the first and second shutoff valves 34, 36 may also be closed, and the exhaust shutoff valve 52 may be fully opened.
[0035] Figure 2 A curve diagram is shown in which the rotational speed of the first compressor 8 is plotted against time. Different scenarios are shown there. Initially, the first compressor 8 is in a stationary state 54, i.e. the rotational speed is zero. Then, the first compressor 8 is accelerated to a first rotational speed 56. This is always done with the same, preferably maximum, rotational speed gradient. After reaching the first rotational speed 56, a first rotational speed gradient is selected. Here, if the probability that the rotor 22 can rotate freely is greater based on the environmental parameters and / or operating parameters of the fuel cell system 2, the first rotational speed gradient value is selected. Then, the first compressor 8 is accelerated to a second rotational speed 58 (path I) with the aid of the first rotational speed gradient value. On the contrary, if the probability that the rotor 22 is blocked is greater, it is accelerated to the second rotational speed 58 (path II) with a lower second rotational speed gradient value. During the acceleration to the second rotational speed 58, it is checked whether the rotor 22 rotates. If this is the case, it is accelerated to the maximum starting speed 60, wherein, for this purpose, the maximum rotational speed gradient (path III and path IV) is selected independently of the previous evaluation of the state of the rotor 22. However, if it is determined that the rotor 22 is blocked, the second rotational speed 58 is maintained, wherein it is repeatedly checked whether the rotor 22 is rotating freely.
[0036] After reaching the maximum starting speed 60 or after repeatedly determining that the rotor 22 is blocked, the first compressor 8 adopts an idling speed. When the rotor 22 is rotating, the idling speed 62 is preferably less than the idling speed 64 when the rotor 22 is blocked. Preferably, the idling speed 64 is large enough to allow the loose, previously blocked rotor 22 to be started. However, in this case, the idling speed 64 when the rotor 22 is blocked is less than the maximum permissible speed 66 when the rotor 22 is blocked.
[0037] In this case, idling speed 62 is sufficiently high that rotating rotor 22 at least follows its minimum speed required in order to protect the gas bearings of rotor 22 .
[0038] The idling speed 62 is also greater than or equal to the minimum permissible speed of the rotor 14 in order to protect the gas bearings of the rotor 14 .
[0039] The dashed line indicates that a transition directly to the load point is also possible. In the case of a freely rotating rotor 22 , the first operating range 68 is greater than the second operating range 70 in the case of a blocked rotor 22 .
[0040] exist Figure 3a and 3b 2 shows the results of a simulation of two starting processes, in which it was assumed that the rotor 22 rotates freely. Figure 3a , a relatively high maximum starting speed of the first compressor 8 is assumed, wherein the speed curve of the first compressor 8 is denoted by reference numeral 72. The resulting speed curve 74 of the rotor 22 remains at zero for a very short time until the starting torque is overcome, after which the speed of the rotor 22 continues to increase. Figure 3b In the embodiment, the maximum starting speed of the first compressor 8 is slightly smaller, so that the speed of the rotor 22 increases slightly more slowly. Figure 3a It is shown that the rotational speed of the first compressor 8 increases significantly more, which leads to a significant increase in the rotational speed of the rotor 22 and to a greater acceleration.
Claims
1. A method for starting a compressor assembly (4) of a fuel cell system (2), the compressor assembly (4) having at least one first compressor (8) which can be operated electrically and a second compressor (18) arranged downstream, the second compressor being coupled via a rotor (22) to a turbine (20) arranged in a cathode path of the fuel cell system (2), the method comprising the following steps: - starting the at least one first compressor (8) and accelerating the at least one first compressor (8) to a first speed (56), the first speed corresponding to at least one idling speed of the at least one first compressor (8), - selecting a first rotational speed gradient from the first rotational speed gradient value and the second rotational speed gradient value, wherein: The first speed gradient value is greater than the second speed gradient value, - accelerating the at least one first compressor (8) from the first speed (56) to a second speed (58) at the first speed gradient, - during acceleration to the second speed, checking whether the rotor (22) rotates freely or whether the rotor (22) is blocked, - if the rotor (22) rotates freely, accelerating the at least one first compressor (8) to a maximum starting speed (60) by means of a second speed gradient, or maintaining said second speed (58), repeatedly checking rotation, and if said rotor (22) is free-turning, accelerating said at least one first compressor (8) to said maximum starting speed (60), wherein if the probability that the rotor (22) of the turbine (20) is not blocked is greater, the first speed gradient value is selected from environmental parameters and operating parameters of the fuel cell system (2), and If the probability that the rotor (22) of the turbine (20) is stuck is greater, the second speed gradient value is selected.
2. The method according to claim 1, further comprising: - before starting the at least one first compressor (8) or directly after starting the at least one first compressor, closing the turbine bypass (48).
3. The method according to claim 1 or 2, further comprising: - before starting the at least one first compressor (8) or directly after starting the at least one first compressor, opening a fuel cell bypass (40), wherein the fuel cell bypass (40) directs compressed intake air into an exhaust path (28) upstream of the turbine (20) in front of a cathode inlet of the fuel cell system (2).
4. The method according to any one of the preceding claims, in, The second rotation speed gradient value is variable and decreases when the ambient temperature decreases or the temperature inside the compressor assembly (4) decreases.
5. The method according to any one of the preceding claims, in, The second speed is selected such that, if the rotor (22) is blocked, pumping of the at least one first compressor (8) is prevented.
6. The method according to any one of the preceding claims, in, The at least one first compressor (8) is accelerated to the second speed (58) in a plurality of speed steps, which are each maintained for a predetermined time interval, wherein the check is performed during the time interval.
7. The method according to any one of the preceding claims, further comprising: - if the rotor (22) has reached at least one minimum rotor speed, the at least one first compressor (8) adopts a predefined or predefined operating speed, or If the rotor (22) is blocked, the operating restrictions on the fuel cell system (2) are maintained and the predefined or predefinable operating speed is adopted while limiting to a limited maximum speed.
8. A fuel cell system (2), comprising: - a fuel cell stack (26), a compressor assembly (4) having at least one first compressor (8) which can be operated electrically and a second compressor (18) which is arranged downstream and which is coupled via a rotor (22) to a turbine (20) which is arranged in the cathode path of the fuel cell system (2), and - a control unit (3) for controlling the fuel cell system (2), in, The fuel cell system (2) is designed to carry out a method for starting the compressor assembly (4) by means of the control unit (3), the method comprising the following steps: - starting the at least one first compressor (8) and accelerating the at least one first compressor (8) to a first speed (56), the first speed corresponding to at least one idling speed of the at least one first compressor (8), - selecting a first rotational speed gradient from a first rotational speed gradient value and a second rotational speed gradient value, wherein the first rotational speed gradient value is greater than the second rotational speed gradient value, - accelerating the at least one first compressor (8) from the first speed (56) to a second speed (58) at the first speed gradient, - during acceleration to the second rotational speed (58), checking whether the rotor (22) rotates freely or whether the rotor (22) is blocked, - if the rotor (22) rotates freely, accelerating the at least one first compressor (8) to a maximum starting speed (60) by means of a second speed gradient, or maintaining said second speed (58), repeatedly checking rotation, and if said rotor (22) is free-turning, accelerating said at least one first compressor (8) to said maximum starting speed (60), wherein if the probability that the rotor (22) of the turbine (20) is not blocked is greater, the first speed gradient value is selected from environmental parameters and operating parameters of the fuel cell system (2), and If the probability that the rotor (22) of the turbine (20) is stuck is greater, the second speed gradient value is selected.
9. The fuel cell system according to claim 8, further comprising: - turbine bypass (50), Therein, the control unit (3) is designed to close the turbine bypass (50) before starting the at least one first compressor (8) or directly after starting the at least one first compressor.
10. The fuel cell system according to claim 8 or 9, further comprising: - a fuel cell bypass (38), Therein, the control unit (3) is designed to open the fuel cell bypass (38) before starting the at least one first compressor (8) or directly after starting the at least one first compressor.