Maiden Application of Ziegler-Nichols Method to AGC of Distributed Generation System

 Abstract

 This paper deals with the load frequency control of Distributed Generation Systems (DGS) consisting of Wind, Solar and Diesel Generator. The Diesel Generator is controlled either by P or PI or PID controller to inject regulated amount of real power to the power system based on its rating. As a result it regulates the mismatch between the real power generation and the load which will lead to a minimum power and frequency deviations. A systematic way of deciding frequency bias parameter along with tuning the gains of the Proportional, Integral and Derivative controller (PID) based on Ziegler-Nichols method and ITSE performance criterion is proposed. The simulation studies are carried out for different types of controllers, and disturbances and it is found that it regulates the frequency with less number of oscillations, minimum peak over shoot, and settling time in the case of PID controller.

Index Terms—Distributed Generation Systems (DGS), Proportional, Integral and Derivative Control (PID), ZieglerNichols method, Optimization methods, Tuning, Frequency Control, Diesel Generators, Wind and Solar, Simulation Analysis.

BLOCK DIAGRAM

Fig. 1. The Block diagram of the Distribution Generation System with Diesel Generator, Wind, Solar power supply and Power System.

SIMULATION RESULTS

Fig. 2. Simulation results of case 1 when wind (0.6 pu), solar (0.3 pu) constant and change in load (0.9 to 0.95 pu) at 100sec : (a) Power Demand and Power Supply in pu (b) Power generated by diesel generator in pu (c) Frequency deviation in Hz.

 

Fig. 3. Simulation results of case 2 when Load (0.9 pu), solar (0.3 pu) constant and change in wind power (0.6 to 0.4 pu) at 100sec : (a) Power Demand and Power Supply in pu (b) Power generated by diesel generator in pu (c) Frequency deviation in Hz.

Fig. 4. Simulation results of case 3 when Load (0.9 pu), wind (0.6 pu) constant and change in solar power (0.3 to 0.2 pu) at 250sec : (a) Power Demand and Power Supply in pu (b) Power generated by diesel generator in pu (c) Frequency deviation in Hz.

CONCLUSION

In this paper a systematic approach for tuning of PID controllers in DGS and calculation of optimal frequency bias are presented. The robustness of the proposed controller is checked with different case studies. The simulation studies of DGS with PID controller shows a better performance in terms of time domain specifications: rise time, peak over shoot, peak time, settling time, and steady state error, than P and PI controllers. When the load or power generation changes occur in the DGS, the PID controller acts such that the Diesel Generator will compensate for the required power. This resulted in the minimum oscillations in the frequency and power. Finally the PID controllers stabilize the system quickly with zero steady state error in less settling time. The frequency bias calculation is very important in the power system dynamics and played a key role in controller gains. This factor directly effects the individual components like Diesel Generators and finally overall performance of the DGS. So the selection of frequency bias is very crucial and is addressed in this paper.

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