Power control method of fuel cell system
By setting a virtual target power and adjusting the integral constant Ki in the fuel cell system, the stack current overshoot problem is solved, and the system stability and noise reduction are achieved.
Patent Information
- Application Number
- CN202510835468.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-06-20
- Publication Date
- 2025-09-26
AI Technical Summary
When the power load of existing fuel cell systems changes, the stack current overshoots, causing system instability and increased noise.
By setting the virtual target power and dynamically adjusting the integral constant Ki, the rate of change of the stack current is controlled to avoid current overshoot.
The operating stability of the fuel cell system is improved and the noise is reduced.
Smart Images
Figure CN120709430A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of fuel cell power control, and in particular to a power control method for a fuel cell system. Background Art
[0002] like Figure 1 As shown, the fuel cell system mainly consists of the following parts: a fuel cell stack 1, a hydrogen subsystem 2, an air subsystem 3, a cooling subsystem 4 and a boost DC / DC (direct current-to-direct current converter) 5. The air subsystem mainly includes an air compressor 31 and a back pressure valve 32.
[0003] When the fuel cell system power changes, the boost DC / DC 5 controls the load current of the fuel cell stack 1. The hydrogen subsystem 2, air subsystem 3, and cooling subsystem 4 respond to the changes in operating parameters caused by the current change, including air flow, hydrogen pressure, and cooling water temperature. The air subsystem 3 controls the air flow by controlling the speed of the air compressor 31. When the fuel cell power increases or decreases rapidly, the IV characteristic will deviate from the IV curve under stable power. Figure 2 As shown in the figure, when the load is rapidly increased, the IV characteristic is lower than the stable IV curve, and when the load is rapidly decreased, the IV characteristic is higher than the stable IV curve. This is because there is a transmission resistance of the reactant gas in the membrane electrode, and the gas concentration changes more slowly than the current response.
[0004] Due to the above reasons, existing fuel cell systems have the following defects and deficiencies when the power load changes:
[0005] When the load is increased or decreased quickly, the stack current will overshoot. Figure 3 As shown in the figure, under load power condition, when the actual power reaches the target power, once the current stops increasing, the voltage will rise again, and the current must be adjusted back, and the fuel cell stack gradually reaches stable IV performance, so the current produces an overshoot higher than the final value; under load power condition, when the actual power reaches the target power, once the current stops decreasing, the voltage will decrease, and the current must rise again, and the fuel cell stack gradually reaches stable IV performance, so the current produces an overshoot lower than the final value.
[0006] This phenomenon, caused by the inherent characteristics of the fuel cell stack, results in current overshoot without power overshoot. Simply adjusting the power control parameters makes it difficult to achieve satisfactory results. This overshoot not only leads to current instability during power control, but also to current-dependent overshoot in various operating parameters, such as compressor speed. This can also cause instability in auxiliary systems and increase noise.
[0007] Therefore, the existing technology still needs to be improved and developed. Summary of the Invention
[0008] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a power control method for a fuel cell system, aiming to solve the problem that when the power load of the existing fuel cell system changes, the stack power does not overshoot but the current overshoots.
[0009] The technical solutions of the present invention are as follows:
[0010] A power control method for a fuel cell system, comprising the steps of:
[0011] When the fuel cell system needs to be loaded with power, the actual target loading power P2 and the current power P of the fuel cell system are obtained, and a virtual target loading power P1 is set with reference to the actual target loading power P2 and the current power P, wherein P<P1<P2;
[0012] According to the difference between the virtual target load power P1 and the current power P, the fuel cell system stack current is adjusted to load power. When the current power P of the fuel cell system is loaded to P1, the integral constant K is reduced. i To reduce the rate of increase of the stack current, until the current power P is loaded to P2, the integral constant K is restored. i Output stack current;
[0013] When the fuel cell system needs to reduce power, the actual target load reduction power P4 is obtained, and the virtual target load reduction power P3 is set with reference to the actual target load reduction power P4 and the current power P, wherein P4<P3<P;
[0014] According to the difference between the virtual target load reduction power P3 and the current power P, the fuel cell system stack current is adjusted to reduce the load power. When the current power P of the fuel cell system is reduced to P3, the integral constant K is reduced. i To reduce the rate of decrease of the stack current, until the current power P is reduced to P4, the integral constant K is restored. i Output stack current.
[0015] The power control method of the fuel cell system, wherein the stack current of the fuel cell system is adjusted to load power according to the difference between the virtual target load power P1 and the current power P, or the stack current of the fuel cell system is adjusted to reduce power according to the difference between the virtual target load power P3 and the current power P, the formula for adjusting the stack current is: Where u(t) is the controlled output of the stack current, e(t) is the difference between the target load power or target load reduction power and the current power, and K p , K i , K d are the proportional constant, integral constant, and differential constant respectively.
[0016] In the power control method of the fuel cell system, in the step of setting the virtual target load power P1 with reference to the actual target load power P2 and the current power P, P1 = P2*n1, wherein 0.8≤n1<1.
[0017] The power control method of the fuel cell system, wherein the integral constant K is reduced i To reduce the rate of increase of the stack current, the K i To reduce the rate of increase of the stack current.
[0018] In the power control method of the fuel cell system, in the step of setting the virtual target load reduction power P3 with reference to the actual target load reduction power P4 and the current power P, P3 = P4*n2, wherein 1<n2≤1.2.
[0019] The power control method of the fuel cell system, wherein the integral constant K is reduced i To reduce the rate of decrease of the stack current, reduce it to 0.1-0.3 times the K i To reduce the rate of decrease of the stack current.
[0020] Beneficial effect: The fuel cell system power control method provided by the present invention is to suppress the current overshoot caused by the stack characteristics when the power rises and falls rapidly by setting a virtual power target and reducing the integral constant, thereby improving the stability of the fuel cell system operation and reducing noise. BRIEF DESCRIPTION OF THE DRAWINGS
[0021] Figure 1 Schematic diagram of the fuel cell system.
[0022] Figure 2 This graph shows the IV characteristics of a fuel cell deviating from the IV curve at steady power when the fuel cell power is rapidly increased or decreased.
[0023] Figure 3 This is a schematic diagram showing the overshoot of the stack current when the existing technology is used to quickly increase or reduce the power.
[0024] Figure 4 This is a flow chart of a power control method for a fuel cell system according to the present invention.
[0025] Figure 5 This is a schematic diagram showing that when the power control method of the present invention is used to quickly increase or decrease the power, the stack current does not overshoot. DETAILED DESCRIPTION
[0026] The present invention provides a power control method for a fuel cell system. To make the objectives, technical solutions, and effects of the present invention more clear and explicit, the present invention is further described below in detail. It should be understood that the specific embodiments described herein are intended only to illustrate the present invention and are not intended to limit the present invention.
[0027] like Figure 3 As shown, when the prior art is loading (increasing) power, at the moment the actual power reaches the target power, the current stops increasing, causing the voltage to rise. According to power P = U*I, to maintain constant power, the rising voltage U forces the current I to fall back, resulting in an overshoot of the current above the final steady-state value. When unloading (reducing) power, at the moment the actual power reaches the target power, the current stops decreasing, causing the voltage to drop. According to P = U*I, to maintain constant power, the falling voltage U forces the current I to rise back, resulting in an overshoot of the current below the final steady-state value. This current overshoot not only leads to unstable power control of the fuel cell system, but also causes overshoot of current-dependent parameters (such as air compressor speed), thereby causing instability and increased noise in the auxiliary system.
[0028] Based on this, the present invention provides a power control method for a fuel cell system, such as Figure 4 As shown, it includes the steps of:
[0029] S10, when the fuel cell system needs to be loaded with power, obtaining an actual target loading power P2 and a current power P of the fuel cell system, and setting a virtual target loading power P1 with reference to the actual target loading power P2 and the current power P, wherein P<P1<P2;
[0030] S20, according to the difference between the virtual target load power P1 and the current power P, the stack current of the fuel cell system is adjusted to load power. When the current power P of the fuel cell system is loaded to P1, the integral constant K is reduced. i To reduce the rate of increase of the stack current, until the current power P is loaded to P2, the integral constant K is restored. i Output stack current;
[0031] S30, when it is necessary to reduce the load power of the fuel cell system, obtaining an actual target load reduction power P4, and setting a virtual target load reduction power P3 with reference to the actual target load reduction power P4 and the current power P, wherein P4<P3<P;
[0032] S40, according to the difference between the virtual target load reduction power P3 and the current power P, the fuel cell system stack current is adjusted to reduce the load power. When the current power P of the fuel cell system is reduced to P3, the integral constant K is reduced. i To reduce the rate of decrease of the stack current, until the current power P is reduced to P4, the integral constant K is restored.i Output stack current.
[0033] In the present invention, by introducing a virtual target power (P1 or P3) and dynamically adjusting the integral constant K of the stack current control loop, i , during the critical stage close to the target power, the rate of change of the current is actively slowed down, thereby avoiding or significantly weakening the current overshoot phenomenon caused by the stack characteristics (the hysteresis characteristic of voltage changing with current), improving the stability of the fuel cell system operation, and reducing noise.
[0034] Specifically, in step S10, when the control system (usually a PID current controller) receives an external instruction to increase the stack power from the current power P to the actual target load power P2. To prevent current overshoot, the system does not directly aim at P2 for control, but sets an intermediate target, that is, sets the virtual target load power P1, and the value of P1 needs to satisfy P < P1 < P2. The selection of P1 is crucial, and it needs to meet: be close enough to P2 to ensure control efficiency; leave enough space for the measure of slowing down the current growth rate to take effect, that is, the P1 point should be before the critical point on the stack I-V curve where the current increase will cause a significant voltage recovery. The present invention preferably sets P1 = P2 * n1, where 0.8 ≤ n1 < 1.
[0035] In this embodiment, by setting the virtual target load power P1, a large power jump is decomposed into two steps: the first step is to quickly increase to P1, and the second step is to slow down near P1 and smoothly transition to P2. This provides an operation window for subsequently slowing down the current growth rate. It avoids the control system from overly aggressively increasing the current at the beginning and lays a foundation for smoothly transitioning to the final target.
[0036] As an example: the current power P = 50kW, the actual target load power P2 = 100kW, at this time, the virtual target load power P1 = P2 * 0.8 = 80kW can be set. At this time, the initial target of the power load of the control system is no longer 100kW, but 80kW.
[0037] In step S20, first in the rapid increase stage (from P to P with a subscript 1 stage): the control system (usually a PID current controller) calculates the required current reference value according to the difference between the current power P and the virtual target load power P1 (P1 - P). The specific formula for adjusting the stack current is:
[0038] where u(t) is the control output of the stack current, e(t) is the difference between the target load power and the current power, and K p 、K i 、K d are the proportional constant, integral constant, and differential constant respectively; in this stage, the control system uses the normal integral constant Ki , driving the battery stack current to increase rapidly, and the power also rises rapidly.
[0039] When it is detected that the actual power P reaches P1, the control system immediately and significantly reduces the integral constant K of the current control loop. i , for example, K i Reduced to K i _small(Ki_small=K i *α, where 0.1≤α≤0.3, preferably α=0.1). At this time, the proportional term K p and K d Normally, the control system maintains a normal value. During this phase, the control system seamlessly switches the target power from P1 to P2. Because the integral constant is significantly reduced, the control system's integral effect on the power difference (P2-P1) becomes very weak. This means that the control system's current increase command increases very slowly.
[0040] When it is detected that the current power P reaches the actual target load power P2, the control system will reduce the integral constant K i _small restores to normal integration constant K i At this point, the power has reached the target, the current is basically stable near the final value, and the control system enters the steady-state maintenance mode.
[0041] like Figure 5 As described above, in this embodiment, after the current power P reaches the virtual target load power P1, by reducing K i Actively reduce the current increase rate, which makes the process of power increasing from P1 to P2 smoother. The effects achieved by this embodiment include: because the current growth rate slows down, the stack voltage will not immediately and significantly recover after reaching P1 due to the current stopping its rapid increase. Since there is no significant voltage recovery, according to the constraint of P=U*I, there is no need to force the current to be called back to maintain the power unchanged, so that the current can be steadily increased to the final target value with almost no overshoot; the current changes steadily, and the parameters such as the air compressor speed that depend on the current will not fluctuate violently, thereby reducing noise and mechanical stress. Figure 5 As shown in the figure, the current overshoot of the power load is greatly reduced, and the excessive speed of the air compressor can also be suppressed.
[0042] For example, the control system starts to rapidly increase the power toward P1=80kW, and the stack current I increases rapidly. When the power reaches 80kW, the current controller K iDecrease from the normal value (e.g., Ki_normal = 0.5) to Ki_small = 0.05 (α = 0.1). At this time, the control system target switches from 80 kW to 100 kW. At this time, since Ki_small is very small, even though the current power (80 kW) is still 20 kW away from the new target (100 kW), the current reference value I output by the control system ref increases very slowly. As the current I increases slowly, the power P also rises slowly. During this slow rise process, the stack voltage has no chance to rise significantly because the current stops increasing rapidly, and the current can climb slowly and steadily. When the power reaches 100 kW, set K i back to Ki_normal = 0.5. The final effect is that the power reaches 100 kW smoothly, the current I reaches the target value I_100kW smoothly, there is no overshoot peak higher than I_100kW, the speed of the air compressor rises smoothly, and the noise does not increase significantly.
[0043] In step S30, when the control system receives an external instruction to reduce the stack power from the current value P to the actual target load reduction power P4. Similarly, to prevent current overshoot, the control system sets an intermediate target, that is, the virtual target load reduction power P3. The value of P3 is set to satisfy P4 < P3 < P. The selection principle of P3 is similar to P1: close enough to P4 to ensure control efficiency; leave room for the measures to slow down the current deceleration to take effect, that is, the point P3 should be before the critical point on the stack I-V curve where the current decrease will cause a significant voltage drop. In this embodiment, preferably P3 = P4 * n2, where 1 < n2 ≤ 1.2.
[0044] In this embodiment, by setting the virtual target load reduction power P3, a large power drop is decomposed into two steps: the first step is to quickly reduce to P3, and the second step is to slow down near P3 and smoothly transition to P4. This can prevent the control system from reducing the current too aggressively at the beginning and lay a foundation for smoothly transitioning to the final target P4.
[0045] As an example: the current power P = 100 kW, the actual target load reduction power P4 = 50 kW. At this time, the virtual target load reduction power P3 = P4 * 1.2 = 60 kW can be set. At this time, the initial target of the power load reduction of the control system is no longer 50 kW, but 60 kW.
[0046] In step S40, first in the rapid decline stage (from P to P3 stage): the control system calculates the required current reference value according to the difference between the current power P and the virtual target load reduction power P3 (P3 - P). The specific formula for adjusting the stack current is: where u(t) is the control output of the stack current, e(t) is the difference between the target load reduction power and the current power, K p 、K i, K d They are proportional constant, integral constant and differential constant respectively; in this stage the control system uses the normal integral constant K i (denoted as K i _normal), the driving current of the battery stack decreases rapidly, and the power also decreases rapidly.
[0047] When it is detected that the current power P reaches P3, the control system immediately significantly reduces the integral constant K of the current control loop i , for example, K i Reduced to K i _small(Ki_small=K i *α, where 0.1≤α≤0.3, preferably α=0.1). At this time, the proportional term K p and K d Normally, the control system switches the target power from P3 to the final target P4 seamlessly. i The integral effect of the control system on the power deviation (P4-P3) becomes very weak, which means that the control system's instruction to reduce the current increases very slowly (ie, the speed of current reduction slows down).
[0048] When it is detected that the current power P reaches the final target P4, the control system will reduce the integral constant K i _small restores to normal integration constant K i At this point, the power has reached the target, the current is basically stable near the final value, and the control system enters the steady-state maintenance mode.
[0049] like Figure 5 As shown, in this embodiment, when the current power reaches the virtual target load reduction power P3, by reducing K i Actively reduce the rate of current reduction, which makes the process of power decreasing from P3 to P4 smoother. Because the current deceleration slows down, the stack voltage will not drop immediately and significantly after reaching P3 due to the current stopping its rapid decrease; since there is no significant voltage drop, according to the constraint of P=U*I, there is no need to force the current to rebound to maintain the power unchanged, so that the current can be reduced to the final target value smoothly and almost without undershoot; the current changes smoothly, and parameters such as the air compressor speed decrease smoothly, avoiding surge or noise caused by the speed being too low and suddenly rebounding. Figure 5 As shown in the figure, the current overshoot of power reduction is greatly reduced, and the air compressor speed can also be suppressed from being too low.
[0050] For example, the control system starts to reduce the power rapidly toward P3=60kW, and the stack current I decreases rapidly. When the power reaches 60kW, the current controller K iFrom the normal value (such as Ki_normal = 0.5) to Ki_small = 0.05. At this time, the control system's target switches from 60kW to 50kW. Since Ki_small is very small, even if the current power (60kW) is still 10kW away from the new target (50kW) (needs to decrease), the current reference value output by the control system decreases very slowly. The current I decreases slowly, and the power P also decreases slowly. During this slow decrease, the stack voltage has no chance to drop significantly because the current stops decreasing rapidly, and the current can be reduced slowly and steadily. When the power reaches 50kW, K i Restore Ki_normal to 0.5. The final effect is: the power reaches 50kW smoothly, the current I reaches the target value I_50kW smoothly, and there is no dip below I_50kW. The air compressor speed decreases smoothly, and the system runs quieter and more stable.
[0051] To sum up, the fuel cell system power control method provided by the present invention is to suppress the current overshoot caused by the stack characteristics when the power rises and falls rapidly by setting a virtual power target and reducing the integral constant, thereby improving the stability of the fuel cell system operation and reducing noise.
[0052] It should be understood that the application of the present invention is not limited to the above examples. For those skilled in the art, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.
Claims
1. A power control method for a fuel cell system, characterized in that: Including steps: When the fuel cell system needs to be loaded with power, the actual target loading power P2 and the current power P of the fuel cell system are obtained, and a virtual target loading power P1 is set with reference to the actual target loading power P2 and the current power P, wherein P<P1<P2; According to the difference between the virtual target load power P1 and the current power P, the fuel cell system stack current is adjusted to load power. When the current power P of the fuel cell system is loaded to P1, the integral constant K is reduced. i To reduce the rate of increase of the stack current, until the current power P is loaded to P2, the integral constant K is restored. i Output stack current; When the fuel cell system needs to reduce power, the actual target load reduction power P4 is obtained, and the virtual target load reduction power P3 is set with reference to the actual target load reduction power P4 and the current power P, wherein P4<P3<P; According to the difference between the virtual target load reduction power P3 and the current power P, the fuel cell system stack current is adjusted to reduce the load power. When the current power P of the fuel cell system is reduced to P3, the integral constant K is reduced. i To reduce the rate of decrease of the stack current, until the current power P is reduced to P4, the integral constant K is restored. i Output stack current.
2. The power control method of the fuel cell system according to claim 1, characterized in that: In the step of adjusting the stack current of the fuel cell system to load power according to the difference between the virtual target load power P1 and the current power P, or adjusting the stack current of the fuel cell system to reduce power according to the difference between the virtual target load power P3 and the current power P, the formula for adjusting the stack current is: Where u(t) is the controlled output of the stack current, e(t) is the difference between the target load power or target load reduction power and the current power, and K p , K i , K d are the proportional constant, integral constant, and differential constant respectively.
3. The power control method of the fuel cell system according to claim 1, characterized in that: In the step of setting the virtual target load power P1 with reference to the actual target load power P2 and the current power P, P1=P2*n1, wherein 0.8≤n1<1.
4. The power control method of the fuel cell system according to claim 3, characterized in that: By reducing the integration constant K i To reduce the rate of increase of the stack current, the K i To reduce the rate of increase of the stack current.
5. The power control method of the fuel cell system according to claim 1, characterized in that: In the step of setting the virtual target load reduction power P3 with reference to the actual target load reduction power P4 and the current power P, P3=P4*n2, wherein 1<n2<1.
6. The power control method of the fuel cell system according to claim 5, characterized in that: By reducing the integration constant K i To reduce the rate of decrease of the stack current, reduce it to 0.1-0.3 times the K i To reduce the rate of decrease of the stack current.