Ziegler-Nichols based Controller Parameters Tuning for Load Frequency Control in a Microgrid

ABSTRACT

This paper deals with the load frequency control of a small scale microgrid consisting of wind, solar, diesel generator and fuel cell as power generating sources and battery, flywheel and aqua electrolyzer as energy storage elements. To improve the load frequency control, the controllers are properly tuned so as to reduce the mismatch between the real power generation and the load demand leading to minimum power and frequency deviations. A systematic approach to obtain frequency bias parameter followed by tuning the gains of Proportional, Integral and Derivative controller (PID) using Integral Square Time Error evaluation criterion (ITSE)and Ziegler Nichols method respectively is proposed. The simulation studies are carried out for different cases and it is found that the dynamic responses of the frequency and power of the microgrid is quite acceptable.

INDEX TERMS—Automatic generation control, frequency and power deviations ,proportional, integral and derivative Control (PID), integral square time error evaluation criterion (ITSE), simulation analysis, Ziegler-Nichols method.

BLOCK DIAGRAM:

Fig. 1. The block diagram of the microgrid with primary sources : solar, wind energy system and secondary sources: diesel generators, fuel cell, aqua electrolyzer, battery, flywheel and power system.

SIMULATION RESULTS:

Fig. 2. Simulation results of Case 1: (a) Supply power PS (b) Power supply form diesel generator Pdg (c) Fuel cell Pf c (d) Aqua electrolyzer Pae (e) Battery Pbat (f) Flywheel Pfw (g) Error in power supply ∆P (h) Frequency deviation of power systems ∆f

Fig. 3. Simulation results of Case 2: (a) Supply power PS (b) Power supply form diesel generator Pdg (c) Fuel cell Pf c (d) Aqua electrolyzer Pae (e) Battery Pbat (f) Flywheel Pfw (g) Error in power supply ∆P (h) Frequency deviation of power systems ∆f

Fig. 4. Simulation results of Case 3: (a) Supply power PS (b) Power supply form diesel generator Pdg (c) Fuel cell Pf c (d) Aqua electrolyzer Pae (e) Battery Pbat (f) Flywheel Pfw (g) Error in power supply ∆P (h) Frequency deviation of power systems ∆f.

CONCLUSION

In this paper a systematic approach for tuning of PID controllers in microgrid and calculation of optimal frequency bias are presented. The frequency bias calculation is an important aspect in the power system dynamics and plays a key role in controller gains. This factor directly effects the individual components and subsequently the overall performance of the microgrid. So the selection of frequency bias is very crucial and is addressed in this paper. The tuning of the PID controller through Zeigler Nichols approach is quite robust to tackle different types of disturbances. The simulation analysis of microgrid with PID controller shows acceptable dynamic performance with zero steady state error. It is also found that when the load is less than the power generated by the primary sources the excess power goes into the battery and flywheel. Similarly when load is more than the power generated by the primary sources, the excess power requirement is mitigated by diesel generator and fuel cell. Thus, the controllers work in coordination with the demand from load to obtain a proper energy management scenario.

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