CN105375046A - Load power switching method for solid oxide fuel cell - Google Patents

Abstract

The invention discloses a safe and effective control method for a solid oxide fuel cell during external load power switching. On the basis that static analysis is carried out to obtain optimal operating points (I, BP, AR and FU) when a system works at fixed load power, a method for solving the problems of fuel deficit and quick tracking of the load power, namely a parabolic open-loop double step current pre-control power switching method is provided when the load power is switched. According to the safe and effective control method, the problem of fuel deficit and the problem of quick tracking of the load power are effectively solved; an safe, efficient and stable quick load tracking of an SOFC system is achieved.

Description

A kind of Solid Oxide Fuel Cell bearing power changing method

Technical field

The invention belongs to field of fuel cell technology, more specifically, relate to a kind of Solid Oxide Fuel Cell bearing power changing method.

Background technology

The energy and environment are the two large problems that the world today faces, and Solid Oxide Fuel Cell (SolidOxideFuelCell, SOFC), as a kind of efficient, clean generation technology, has good application prospect.Solid Oxide Fuel Cell is a kind of is directly the Blast Furnace Top Gas Recovery Turbine Unit (TRT) of electric energy by the chemical energy be stored in fuel and oxidant, do not produce this pilot process of heat energy, its energy conversion efficiency does not limit by Carnot cycle, and theoretical efficiency can reach 80-90%, and reality can reach 45-70%.Compared with the generation modes such as traditional firepower, the features such as have generating efficiency high, noise is little, environmental friendliness low emission.

As shown in Figure 1, independently SOFC system comprises pile, heat exchanger, bypass valve, air blast, combustion chamber, control cubicle.Chinese patent CN103236555A describes the Solid Oxide Fuel Cell construction system of complete set and the method for thermoelectricity Collaborative Control thereof in detail, improves the efficiency of system, ensure that the useful life of pile.Chinese patent CN103969593A analyzes a kind of method determining SOFC system parameters, by carrying out static analysis to system, find a job the system optimal operating point under different capacity, within making system temperature maintain safe range enabling system effectiveness maximized while, ensure system stability, run efficiently.But how these patents all do not ensure fast when power changes, load tracking safely and efficiently, and how to go during changed power to avoid fuel in debt.

Summary of the invention

For the safety and efficiently sex chromosome mosaicism of SOFC system when load dynamic mapping, the invention provides a kind of Solid Oxide Fuel Cell bearing power changing method, the fail safe of angle resolved systems of rising from bearing power and the performance of efficient stable, avoid that fuel occurs in debt simultaneously.

By static analysis, obtain on the basis of system optimal operating point.Analyse in depth open loop dynamic response characteristic when its exterior bearing power switches, the critical problem that particularly system is potential, such as, transmission delay in dynamic response process, system effectiveness, fast power follows the tracks of situation and fuel problem in debt, and then carries out control strategy and Controller gain variations targetedly, realizes SOFC system safety, efficiently, stably Fast Load tracking is carried out.

Two problems is there is in the handoff procedure of solid oxide fuel battery system:

First problem: fuel problem in debt.Fuel is in debt, and namely pile outlet fuel component equals 0.Research finds when power output generation step rises, if gas supply not in time raising can make system because of fuel deficit and shut down, damage, the deficit of solution fuel is the emphasis that the present invention carries out studying.

Second Problem: the quick tracking problem of power.Improve system power responsiveness speed, make system power fast and effeciently follow the tracks of external loading.

The response process of power response curve can be divided into two stages: first stage is the quick response caused by electrochemical properties, i.e. electrochemical response stage, and its response time is in level or hundred seconds levels second; Second stage slowly changes by temperature the temperature response stage caused, and its response time is kilosecond level even ten thousand seconds levels.

If directly switched, slowly, and there is fuel problem in debt in its load tracking; in order to solve this two problems; coupling system power response characteristic, its basic ideas adopt parabola open loop two step electric current pre-control power changing method, that is: at power by initial power be switched to target time, find a middle power make by initial power be switched to middle power electrochemical response can meet target power demand, then by middle power be switched to target power in these two power handoff procedures, keep output current conditioning signal to be the throwing camber line signal that slope increases gradually, power is slowly increased.

In order to study the open loop dynamic characteristic of SOFC electricity generation system, the open loop dynamic characteristic response that bearing power step rises is analyzed.Such as, change from half load 2.5Kw to full load 5Kw at 50000s, observe the exporting hydrogen flow of its each node of monocell sheet (5 nodes), find except first node exit place hydrogen component is not that except 0, other nodes all produce fuel deficit.Owing to increasing when external load demands, by the consumption of instantaneous increasing for fuel, and often there is certain time delay in the transmission of gas, thus the fuel causing partial period is in debt, and the work safety of influential system is with stable.Under hydrogen supply exists time delay situation, when being switched to high capacity by low load, single step step strategy can not be adopted, need the rational changing method of targeted design, to avoid fuel in debt.

Crossing the problems such as slow to solve fuel deficit and power tracking in load increase process, proposing a kind of method solving fuel deficit and the quick tracking problem of bearing power, be i.e. parabola open loop two step electric current pre-control power changing method.Its concrete technical scheme is as follows:

The process obtaining power response by experiment can be divided into two stages: first stage is the quick response caused by electrochemical properties, i.e. electrochemical response stage, and its response time is in level or hundred seconds levels second; Second stage slowly changes by temperature the temperature response stage caused, and its response time is kilosecond level even ten thousand seconds levels.

Suppose that SOFC system power is at time t ₀by power switch to then in SOFC system responses process, power stage can be expressed as:

Wherein the power amplification in representative system Chemical response stage, the power amplification of representation temperature response phase.

Under parabola open loop two step electric current pre-control power changing method, consider from switch to optimum point corresponding to it is respectively ( bP ⁰, AR ⁰, FU ⁰) and ( bP ^des, AR ^des, FU ^des); if directly switched; its load tracking slowly; in order to address this problem; there is fuel problem in debt simultaneously; coupling system power response characteristic, its basic ideas retain the electrochemical response stage rapidly response time exactly, reject the stage of temperature response slowly relatively response time.For this reason, the present invention devises open loop two step electric current pre-control power switchover policy: introduce a middle power variable larger than power demand point corresponding optimum point be ( bP ^imdaR ^imd, FU ^imd), and middle power variable meets the following conditions:

$P_{net}^{imd}=P_{net}^0+{\mathrm{\δ}}_1{P}_{{\mathrm{net}}_E}+{\mathrm{\δ}}_1{P}_{{\mathrm{net}}_T}$

Wherein δ P, close to 0, is very little value.

Namely the electrochemical response in handoff procedure is had the approximate recruitment equaling final power

The present invention is divided into two Main Stage power switching and switches: first stage is called switch step, and second stage is called the maintenance stage, and institute is somewhat equal to be switched between optimum point.

The essence of switch step retains the electrochemical reaction response process in SOFC system power response process, system is made to track to rapidly external demand load, the problem that should be noted that in switch step finds the optimal switching time, make it not produce fuel deficit, the optimal switching time of supposing the system under certain power switches is then select switching time all there will not be fuel in debt in switch step.Need emphasis to find two parameters in switch step, one is the switching time making system not produce fuel deficit, and another one makes system carry out the middle power switched it is worthy of note, after switch step completes, system can reach bearing power track demand fast, and namely the time period of its bearing power tracking is close with switching time, supposes at t ₀moment starts to switch, and load is at t _gtime tracking to external load demands, then has

δ t is the time period close to 0.

The main purpose in maintenance stage is under the prerequisite keeping power near external loading power demand, slowly switch to stable state optimal working point ( bP ^des, AR ^des, FU ^des), in the maintenance stage, select different parabola toggle paths, system is at t _gmoment switches, and in this phase process, load tracking remains on target power near value, the maximum tracking error in its tracking mode power response process is weighed:

$Max.e_p=\underset{P_k(a,b)}{max}|P_{net}\left(t\right)-P_{net}^{des}|,k\∈\{1,2,...,K\},t\∈\[t_g,\mathrm{\∞})$

Wherein, P _k(a, b) represents power toggle path, for 5kWSOFC system of the present invention, and regulation Max.e _p≤ ξ, ξ ∈ [0,0.15kW].

Middle power obtained by experimental data with switching time, as shown in Figure 2, according to initial power and target power fig. 2 can be looked into and obtain middle power and switching time.

Generally speaking, compared with prior art, the changing method of parabola two step electric current pre-control combination of the present invention's design achieves SOFC system safety, efficiently, stably carry out, and the handoff procedure that raises speed greatly, overcome the time lag feature of SOFC system Great inertia, truly realize load fast and switch, avoid fuel in debt simultaneously.

Accompanying drawing explanation

Fig. 1 is 5KWSOFC system block diagram in the embodiment of the present invention;

Fig. 2 is pre-control parameter set (a) switching time and (b) middle power switched of Systematical control, and white line represents boundary, represent the in debt switching only considered under power rising operating mode of fuel.

Embodiment

In order to make object of the present invention, technical scheme and advantage clearly understand, below in conjunction with drawings and Examples, the present invention is further elaborated.Should be appreciated that specific embodiment described herein only in order to explain the present invention, be not intended to limit the present invention.In addition, if below in described each execution mode of the present invention involved technical characteristic do not form conflict each other and just can mutually combine.

By the changing method of above-mentioned designed parabola two step electric current pre-control combination, make half load track to external demand load fast to system during the switching of full load, do not have fuel in debt simultaneously.If switch the power of arbitrary load tracking, in pile the severe degree of electrochemical reaction and fuel in debt directly related with the switching rate of electric current, switch step itself and also and system delay, initial power switched middle power switched relevant.

Shown in Fig. 2, under the changing method of parabola two step electric current pre-control combination, switch operating mode, test according to different power, system under specific switching operating mode of finding does not produce the switching time of fuel deficit, system from rise to time the middle power value introduced as can be seen from the figure, with t switching time ₁value set both can as table look-up (look-uptable, the LUT) of Systematical control, index (researchmap) can be found as the parameter in control procedure again.

Suppose that the equation of the process of changing method is for (supposing to carry out when t=50000s power switching, initial power 2.5KW, target power 4.4KW):

I _s(t)＝at ²+bt∈[50000s,50150s]

Wherein t represents the time, a and b for according to determined optional optimization steady state operation point under switching initial point and different stable state form regulating parameter set by matching toggle path.

The changing method of parabola two step electric current pre-control combination, selecting system carries out power switching from 2.5kW to 5kW, selects a=-5.86e-9, b=72.7, if find that switching time is higher than 25s through experiment, all there will not be fuel in debt in principle.

Identical to the optimal switching time finding method of full load with above-mentioned half load, determine during experiment that the searching process of the optimal switching time switched under operating mode can in order to lower the Representation Equation:

$\underset{a,b}{min}\left(t_s\right)$

Make ${\left(X_{H_2}\right)}_j>0,j\∈\{1,2,...,J\}$

Wherein j represents the node index in monocell sheet, and J represents total number of network nodes, represent the molar fraction of hydrogen.

In order to solve the quick tracking problem of load, given power output carries out parabola switching at 50000s from half load to full load, in its handoff procedure, switching time is chosen as 25s, system power increases to about 4.4kW at about 30s fast by 2.5kW, then slowly 5kW is increased to through a few kilosecond, first stage is the quick response caused by electrochemical properties, i.e. electrochemical response stage; Second stage slowly changes by temperature the temperature response stage caused.

So when external loading is from 2.5kW at 50000s (t ₀) to 4.4kW switch, middle power 5kW can be introduced first 5kW is switched to from 2.5kW, by the electrochemical response stage at 30s (t _g) just can reach aims of systems power 4.4kW, this stage is switch step.If hypothetical target load impulsive is reset to 2.5KW at 50000s (t ₀) to 4.4kW switch, and setting surrounding target load 4.4KW permissible error is 100W (Max.e _p=0.1kW) time, namely set 1KW-2KW and all reach switching target.The present invention plans to be divided into two stages with the changing method design of " the shortest in main optimizing index with switching time ":

Fast power ascent stage (switch step): according to the optimal switching time of system middle power carry out parabolic increase between (steady-state optimization operating point) by 2.5KW to 5KW (exceeding desired value 4.4KW) to switch;

Switch the stable state maintenance stage (keeping the stage): when real output reaches 4.45KW (be in and allowed targeted loads scope), carry out subsequently being switched to 4.4KW (steady-state optimization operating point) by 5KW;

According to above step, according to set tracking error, select suitable electric current parabola as switch the maintenance stage operating parameter (as, select a=-8.79e-9, b=80.0), overall switching time only needs about 30s, and its switching time is within accepting scope.

Those skilled in the art will readily understand; the foregoing is only preferred embodiment of the present invention; not in order to limit the present invention, all any amendments done within the spirit and principles in the present invention, equivalent replacement and improvement etc., all should be included within protection scope of the present invention.

Claims (4)

1. a solid oxide fuel battery system bearing power changing method, is characterized in that, described method comprises the steps:

Adopt parabola open loop two step electric current pre-control power changing method, at power by initial power be switched to target power time, find a middle power make by initial power be switched to middle power electrochemical response meet target power demand, then by middle power be switched to target power in these two power handoff procedures, keep output current conditioning signal to be the throwing camber line signal that slope increases gradually, power is slowly increased.

2. solid oxide fuel battery system bearing power changing method according to claim 1, is characterized in that, described parabola open loop two step electric current pre-control power changing method is specially:

If SOFC system power is at time t ₀by power switch to then in SOFC system responses process, power stage can be expressed as: wherein the power amplification in representative system Chemical response stage, the power amplification of representation temperature response phase;

Under parabola open loop two step electric current pre-control power changing method, consider from switch to optimum point corresponding to it is respectively with introduce a middle power variable larger than power demand point corresponding optimum point is and middle power variable meets the following conditions:

$P_{net}^{imd}=P_{net}^0+{\mathrm{\δ}}_1{P}_{{\mathrm{net}}_E}+{\mathrm{\δ}}_1{P}_{{\mathrm{net}}_T},$ Wherein $\mathrm{\δ}P=|{\mathrm{\δ}}_1{P}_{{\mathrm{net}}_E}-({\mathrm{\δP}}_{{\mathrm{net}}_E}+{\mathrm{\δP}}_{{\mathrm{net}}_T})|;$

Namely the electrochemical response in handoff procedure is had the approximate recruitment equaling final power ${\mathrm{\δP}}_{{\mathrm{net}}_E}+{\mathrm{\δP}}_{{\mathrm{net}}_T}.$

3. solid oxide fuel battery system bearing power changing method according to claim 2, is characterized in that:

Power switching is divided into two stages: first stage is called switch step, and second stage is called the maintenance stage, and institute is somewhat equal to be switched between optimum point, and its handoff procedure is as follows:

Wherein:

$P_{net}^0\∈\[1kW,5kW)$

$P_{net}^{imd}\∈(1kW,6kW\]$

$P_{net}^{des}\∈(1kW,5kW\]$

$P_{net}^{imd}>P_{net}^{des}>P_{net}^0$

The essence of switch step retains the electrochemical reaction response process in SOFC system power response process, makes system track to rapidly external demand load and do not produce fuel deficit; Need emphasis to find two parameters in switch step, one is the throwing camber line current switching time making system not produce fuel deficit, and another one is the middle power carrying out switching suppose at t ₀shi Jinhang switches in t _gin time, completes and enters the maintenance stage;

The main purpose in maintenance stage is under the prerequisite keeping power near external loading power demand, slowly switches to stable state optimal working point in the maintenance stage, select different parabola toggle paths, system is at t _gmoment switches, and in this phase process, load tracking remains on target power near value, the maximum tracking error in its tracking mode power response process is weighed:

$Max.e_p=\underset{P_k(a,b)}{max}|P_{net}\left(t\right)-P_{net}^{des}|,k\∈\{1,2,...,K\},t\∈\[t_g,\mathrm{\∞})$

Wherein, P _k(a, b) represents power toggle path, for 5kWSOFC system of the present invention, and regulation Max.e _p≤ ξ, ξ ∈ [0,0.15kW].

4. the two step of the open loop according to any one of claims 1 to 3 electric current pre-control power switchover policy, is characterized in that:

Middle power obtained by experimental data with switching time.