Based on a thing that it is difficult to choose the parameters of active disturbance rejection control for the non-linear ALSTOM gasifier, multi-objective optimization algorithm is applied in the choose of parameters. Simulation results show that performance tests in load change and coal quality change achieve better dynamic responses and larger scales of rejecting coal quality disturbances. The study provides an alternative to choose parameters for other control schemes of the ALSTOM gasifier.
Integrated gasification combined cycle (IGCC) power plants are being developed to provide environmentally clean and efficient power from coal. GEC ALSTOM developed a small-scale prototype integrated plant, based on air-blown gasification cycle (ABGC). The gasifier as a component of the ABGC is a highly coupled multi- variable system with five inputs and four outputs and is found to be particularly difficult to control.
In 1997, the ALSTOM Energy Technology Center issued an open challenge to the UK Academic Control Community to develop advanced control techniques for the linear model of the ALSTOM gasifier. The “challenge information pack” [
Many advanced control approaches have been applied in the control of the non-linear ALSTOM gasifier, such as
The non-dominated sorting genetic algorithm-II (NSGA-II) [
In the paper, based on the analysis of multi-objective optimal algorithm, NSGA-II is applied in the choice of parameters for ADRC schemes of the ALSTOM gasifier. Simulation results show that performance tests in load change and coal quality change achieve better dynamic responses and larger scales of rejecting coal quality disturbances. The content is arranged as follows: Section 2, ALSTOM gasifier model and control system specification are introduced; Section 3, NSGA-II for ADRC scheme of the ALSTOM gasifier is proposed, including the chose of objective function of multi-objective optimization, the results of the optimization and the performance tests; conclusion is given in Section 4.
The gasifier is a non-linear, multi-variable component, and provided in the Challenge II of ALSTOM gasifier benchmark problem [
The control specification of the non-linear gasifier are listed as follows.
1) Pressure disturbance tests: A downstream pressure disturbance Psink, choosing from step disturbance of −0.2 bar or sine wave disturbance of amplitude 0.2 bar and frequency of 0.04 Hz, is applied to the gasifier, running the simulation 300 seconds; and calculate IAE index for the gas quality Cvgas and gas pressure Pgas over the complete run.
2) Load change tests: Start the system at 50% load in steady state and ramp it to 100% over a period of 600 seconds (5% per minute). The measured load should follow the load demand as closely as possible with minimal over shoot at the end of the ramp. The input constraints need to be adhered to the controller outputs all the time.
3) Coal variation test: Coal quality can change quite significantly depending on its source. It should be changed incrementally within the range ±18%, and any effect on the performance of the controller should be noted.
In the control of the ALSOTM gasifier, the intension is that the performance tests would facilitate the evaluation of the closed-loop systems response to pressure disturbances, load changes and coal quality changes [
In ADRC scheme, the parameter
Moreover, the adding of ADRC gives rise to the order increase of the gasifier, the initial states x0c should be reset, and the initial values u0 of each ADRC can be initialized. The initial values x0c and u0 at three loads can be obtained using the suggested method [
In ADRC scheme, the parameter
The objective function is formulated as follows
where m
Load (%) | x0c | u0 |
---|---|---|
100 | [0.9779 17.4391 2.6672 8.6123] | |
50 | [1.1873 12.1251 2.0071 6.8439] | |
0 | [1.5519 6.5583 1.2367 5.1573] |
respectively;
An index of coal quality flexibility was defined as follows [
After multi-objective optimal algorithm has been run six times, a set of parameters are obtained, as shown in Figures 1(a)-(d).
Although the scope of the Y-axis the change of the RIAE indices of the CVgas in
The comparisons of the twelve objective functions and the total RIAE indices among Simm, ADRC2 and MOADRC are listed in
With the parameter set MOADRC, the performance tests of ADRC scheme are done. The simulation results are compared with that of Simm’s, MOPI2 and ADRC2.
Performance Tests(1) Psink disturbance tests
Based on the specification of the ALSTOM gasifier [
Parameter | ADRC2 | MOADRC | Parameter | ADRC2 | MOADRC |
---|---|---|---|---|---|
0.1230 | 0.2063 | 0.2219 | 0.2625 | ||
7 | 14.3158 | 3 | 6.8761 | ||
1000 | 1263.9 | 20000 | 3311.5 | ||
0.5610 | 0.9659 | 0.1451 | 0.1234 | ||
4 | 3.9855 | 1.0328 | 0.8745 | ||
2500 | 2798.8 |
Parameters | f1 | f2 | f3 | f4 | f5 | f6 |
---|---|---|---|---|---|---|
Simm | 45.3820 | 74.6000 | 2.2312 | 6.72830 | 50.9100 | 91.8738 |
ADRC2 | 13.3933 | 0.9332 | 1.4512 | 2.9229 | 16.8375 | 1.2458 |
MOADRC | 9.7081 | 13.5120 | 0.9806 | 2.3448 | 11.8789 | 18.1098 |
Parameters | f7 | f8 | f9 | f10 | f12 | f12 |
Simm | 2.4316 | 8.3613 | 64.5670 | 144.7509 | 3.1002 | 8.7586 |
ADRC2 | 1.9920 | 3.4737 | 24.8631 | 78.0664 | 2.9219 | 4.9765 |
MOADRC | 1.0219 | 2.8156 | 16.8697 | 96.7032 | 1.0620 | 4.1163 |
Parameter | 100% | 50% | 0% | |||
---|---|---|---|---|---|---|
sine | step | sine | step | sine | step | |
Simm | 170.3016 | 46.4952 | 198.0433 | 45.4174 | 275.4846 | 46.4952 |
ADRC2 | 71.2025 | 14.9918 | 87.9738 | 15.4060 | 204.0164 | 21.7982 |
MOADRC | 97.2771 | 15.6089 | 118.9365 | 15.7798 | 228.4470 | 21.7876 |
and sine disturbances at 0% load. The simulation results at 100% and 50% loads are omitted.
(2) Load change test
Load change test of MOADRC are shown in
(3) Coal quality change test
In this test, when the coal quality is changed incrementally (within the range ±18%) with step or sine disturbance at certain load, upper and lower boundary guaranteeing the gasifier in steady state are recorded. The simulation results are shown in
In this study, NSGA-II is introduced to choose the set of control parameters for ADRC scheme of the ALSTOM gasifier. Simulation results with the optimized parameters show that load change and coal quality change achieve relative good dynamics responses, larger scales of rejecting coal quality disturbances. The study also provides an alternative to choose parameters for other control schemes of the ALSTOM gasifier.
Index | Ch_min | T_max | BM_min | BM_end | TPV_coal |
---|---|---|---|---|---|
Unit | (kg) | (K) | (kg) | (kg) | (s) |
Simm | 0 | 1226.1 | 9096.4 | 9629.0 | 118.7 |
MOPI2 | 0 | 1236.8 | 8943.3 | 9627.9 | 115.8 |
ADRC2 | 0.5042 | 1222.0 | 9174.1 | 9646.4 | 177.6 |
MOADRC | 0 | 1222.4 | 9164.5 | 9643.4 | 175.8 |
Load | 100% | 50% | 0% | |||
---|---|---|---|---|---|---|
Disturbance | Sine | Step | Sine | Step | Sine | Step |
Simm | [−18, 6] | [−18, 11] | [0, 11] | [−18, 17] | [−2, 0] | [−18, 18] |
MOPI2 | [−17, 2] | [−18, 11] | [−4, 5] | [−18, 17] | [0, 14] | [−18, 17] |
ADRC2 | [−16, 5] | [−14, 11] | [−18, 7] | [0, 4] | [−17, 16] | [−18, 18] |
MOADRC | [−17, 6] | [−14, 11] | [−18, 8] | [−17, 17] | [−1, 18] | [−18, 18] |
Scheme | Simm | ADRC2 | MOADRC |
---|---|---|---|
JCQ | 137 | 144 | 163 |
This project is supported by the Science & Technology Program of Beijing Municipal Commission of Education (KM201511417012).
Chun’eHuang,ZhongliLiu, (2015) Multi-Objective Optimization for Active Disturbance Rejection Control for the ALSTOM Benchmark Problem. International Journal of Clean Coal and Energy,04,61-68. doi: 10.4236/ijcce.2015.43006