**American Journal of Electrical and Electronic Engineering**

## Effective Micro Grid Stability Under Excitation Limiters in Islanded and Connected Modes

**Sajad Tashakori**^{1}, **Amir Tavakoli**^{2}, **Farzad Mirzaei**^{1,}

^{1}Electrical Department, Shiraz University of Technology, Shiraz, Iran

^{2}Mechanical Department, Islamic Azad University of Shiraz, Shiraz, Iran

### Abstract

In this paper the authors tried to design a under excitation limiter and a power system stabilizer which can operate without any kind of interaction. The under excitation limiter (UEL) is intended to prevent reduction of generator excitation to a level where the steady state stability limit or the stator core end-region heating limit is exceeded. The power system stabilizer (PSS) uses auxiliary stabilizing signals to control the excitation system so as to improve power system dynamic performance.

**Keywords:** power system operation, stability, under excitation limiter

**Copyright**© 2017 Science and Education Publishing. All Rights Reserved.

### Cite this article:

- Sajad Tashakori, Amir Tavakoli, Farzad Mirzaei. Effective Micro Grid Stability Under Excitation Limiters in Islanded and Connected Modes.
*American Journal of Electrical and Electronic Engineering*. Vol. 5, No. 1, 2017, pp 28-33. https://pubs.sciepub.com/ajeee/5/1/5

- Tashakori, Sajad, Amir Tavakoli, and Farzad Mirzaei. "Effective Micro Grid Stability Under Excitation Limiters in Islanded and Connected Modes."
*American Journal of Electrical and Electronic Engineering*5.1 (2017): 28-33.

- Tashakori, S. , Tavakoli, A. , & Mirzaei, F. (2017). Effective Micro Grid Stability Under Excitation Limiters in Islanded and Connected Modes.
*American Journal of Electrical and Electronic Engineering*,*5*(1), 28-33.

- Tashakori, Sajad, Amir Tavakoli, and Farzad Mirzaei. "Effective Micro Grid Stability Under Excitation Limiters in Islanded and Connected Modes."
*American Journal of Electrical and Electronic Engineering*5, no. 1 (2017): 28-33.

Import into BibTeX | Import into EndNote | Import into RefMan | Import into RefWorks |

### At a glance: Figures

### 1. Introduction

Stability of power system is one of the most significant issue in power system operation and planning ^{[1, 2, 3]}. Indeed, stability of the power system is involved in many other electrical problems. For instance in power electronics field, the stability of the system is analyzed in ^{[4, 5, 6]}. In power system operation, the stability of system is foci in ^{[7, 8]}. By adding the renewable energies, the power stability decreased significantly. However, in ^{[9]}, the stability of power system is solved. In ^{[10, 11, 12]} different methods are used to address the power system stability problems [13-25]^{[13]}.

In this paper, coordinated Design of Under-Excitation Limiters and Power System Stabilizers is analyzed. The result proved the high efficiency and performance of the proposed technique. Also, the methods is applied for different stability status. All the simulation and results are done in Matlab software.

To sum up, this paper is organized as follows: Section 2 explained the proposed method to address the problem. In section 3, the simulation results are explained and discussed. Finally, section 4 argued about the conclusion of the research.

### 2. Proposed Method

The simplified Heffron-Phillips model with PSS and UEL control loops were shown in Figure 1. Next figure shows a typical bode plot of prior model.

**Fig**

**ure**

**1,**A typical bode plot of prior model

Also, bode plot for a special case in shown as follows:

**Fig**

**ure**

**2**

**.**A typical bode plot of

In this special case

We can see that the two break points (s1, s2) are typically two decades apart. Stability can be assured if the UEL is tuned in such a way that the cross-over frequency (ωc) is somewhere between the two break points.

As the generator heating time-constant is large compared to those associated with the usual electromechanical modes (0.5-2 HZ), it is necessary for the UEL to achieve a fast response characteristic. So (ωc) should be closer to the first break point in order to ensure adequate phase margin. The PSS is introduced so that a damping torque component is produced over a selected frequency range. The frequency range of interest is around the second break point. As this second break point is about two decades away from the first break point, it can be concluded that the proposed UEL tuning method will result in its control action having little effect on the PSS and vice versa [26-31]^{[26]}.

**Fig**

**ure**

**3**

**.**

**A power system stabilizer transfer function**

### 3. Case Study and Results

Your paper must use a page size corresponding to A4 which is 210mm wide and 297mm long. The margins are set as follows: top= 15 mm, bottom= 15 mm, right=17.5 mm, left = 20 mm. Your paper must be in two column format with a space of 1.93 characters between columns ^{[12, 13, 14, 15]}.

The methods for designing UEL and PSS based on famous below diagrams are mentioned in the paper.

**Fig**

**ure**

**4**

**.**UEL Scheme

Also, the power system stabilize transfer function is shown in the next figure.

The extended excitation system and AVR model were used as shown below.

**Fig**

**ure**

**5**

**.**AVR model of G1

To simulate the prior blocks it’s necessary to calculate (K1-K8) based on steady state power system model. I used of an M-file that shown as below for this matter. The outputs of the below program are K1-K8.

The algorithm in Matlab in defined as follows [16-28]^{[16]}:

*Vd0=0.978;*

*Vq0=0.204;*

*Id0=0.978;*

*Iq0=0.204;*

*Vt0=0.999;*

*Xd=4.53;*

*Xq=Xd;*

*X1d=0.4;*

*X1q=X1d;*

*XT=0.06;*

*XL=0.2;*

*Xe=XT+XL;Ku=2;*

*Tj=6.11;*

*K1=(Vd0-X1d*Iq0)*(Vd0+Xe*Iq0)/(Xe+X1d)+(Vq0-Xe*Id0)*(Vq0+X1q*Id0)/(Xe+X1q);*

*K2=(Vd0+Xe*Iq0)/(Xe+X1d);*

*K3=(Xe+X1d)/(Xe+Xd);*

*K4=(Vd0-Xe*Iq0)*(Xd+X1d)/(Xe+X1d);*

*K5=X1q*Vd0*(Vq0-Xe*Id0)/(Vt0*(Xe+X1q))-X1d*Vq0*(Vd0-Xe*Iq0)/(Vt0*(Xe+X1d));*

*K6=Xe*Vq0/(Vt0*(Xe+X1d));*

*K7=(Vd0*Iq0*(X1d-Xe)+Iq0^2*X1d*Xe-*

*Vd0^2)/(Ku*(Xe+X1d))+(Vq0*Id0*(X1q+Xe)+Id0^2*X1q*Xe-Vq0^2)/(Ku*(Xe+X1q))-*

*((Vd0*Id0+Vq0*Iq0)*(X1d*X1q-Xe^2))/((Xe+X1d)*(Xe+X1q))-*

*((Vd0*Vq0+Iq0*Id0*Xe^2)*(X1d-X1q))/((Xe+X1d)*(Xe+X1q));*

*K8=(Vq0+Xe*Id0)/(Xe+X1d)-(Vd0+Xe*Iq0)/(Ku*(Xe+X1d));*

Where K7 & K8 & K18 & C depend on Ku

*K16=K6-K2*K5/K1;*

*K18=K8-K2*K7/K1;*

*Kg=K1*K3/(K1-K2*K3*K4);*

*A=Tj/(2*pi*60*K1);*

*B=K1*K6/(K1*K6-K2*K5);*

*C=K1*K8/(K1*K8-K2*K7);*

By using the Simulink/MATLAB and the prior information these results could be achieve. From Figure 7 and Figure 8 we understand that the frequency region of the PSS operation is about mid frequency. And also, from Figure 9 it’s clear that the frequency region of the UEL operation is about low frequency. Therefore the designed UEL does not have any interaction with designed PSS. Hence the example serves to illustrate the fact that design of the UEL and PSS can be considered separately as each of the control devices is effective over a different frequency range. Figure 10 describes the effect of the UEL slope Ku on system performance.

This is shown on Figure 10, where it’s clear that changes in Ku have no effect on the low frequency region. When Ku exceeds 6, the changing of Ku does not improve the gain margin significantly. It is desirable to set Ku to as large a value as possible to ensure adequate damping.

For showing the effect of the UEL on the time response characteristic of the generator the following simulation with PSCAD/EMTDC was done. The simulation shows a reactor tripping in 2 sec.

From the prior results, it’s clear that the designed UEL have a suitable effect on the generator stability.

**Fig**

**ure**

**6.**bode plot of

**Fig**

**ure**

**7**

**.**Body plot when XL=1

**Fig**

**ure**

**8**

**.**Body plot when XL=0.1

**Fig**

**ure**

**9**

**.**Body plot when

**Fig**

**ure**

**10**

**.**Body plot when (effect of KU)

**Fig**

**ure**

**1**

**1**

**.**The main structure of the problem

**Fig**

**ure**

**1**

**2**

**.**

**Time Response without UEL**

**Fig**

**ure**

**1**

**3**

**.**Time response with UEL

### 4. Conclusion

It has been shown that the tuning of the UEL and PSS can be carried out separately and without having to consider inter action between the two control loops. Effective control action of the UEL can be achieved by having Ku set to the highest value possible.

### References

[1] | Fogg, B.J, Persuasive technology: using computers to change what we think and do, Morgan Kaufmann Publishers, Boston, 2003, 30-35. | ||

In article | |||

[2] | Hirsh, H., Coen, M.H., Mozer, M.C., Hasha, R. and Flanagan, J.L, “Room service, AI-style,” IEEE intelligent systems, 14 (2). 8-19. Jul.2002. | ||

In article | View Article | ||

[3] | T. Eckes, The Developmental Social Psychology of Gender, Lawrence Erlbaum, 2000. [E-book] Available: netLibrary e-book. | ||

In article | |||

[4] | Bozorgi, Amir Masoud, Vahid Fereshtehpoor, Mohammad Monfared, and Navid Namjoo. “Controller Design Using Ant Colony Algorithm for a Non-inverting Buck–Boost Chopper Based on a Detailed Average Model.” Electric Power Components and Systems 43, no. 2 (2015): 177-188. | ||

In article | View Article | ||

[5] | Bozorgi, Amir Masoud, Majid Sanatkar Chayjani, Reza Mohammad Nejad, and Mohammad Monfared. “Improved grid voltage sensorless control strategy for railway power conditioners.” IET Power Electronics 8, no. 12 (2015): 2454-2461. | ||

In article | View Article | ||

[6] | Mehrtash, Mahdi, Mahdi Raoofat, Mohammad Mohammadi, and Hamidreza Zareipour. “Fast stochastic security‐constrained unit commitment using point estimation method.” International Transactions on Electrical Energy Systems 26, no. 3 (2016): 671-688. | ||

In article | View Article | ||

[7] | Dabbaghjamanesh, M., A. Moeini, M. Ashkaboosi, P. Khazaei, and K. Mirzapalangi. “High performance control of grid connected cascaded H-Bridge active rectifier based on type II-fuzzy logic controller with low frequency modulation technique.” International Journal of Electrical and Computer Engineering (IJECE) 6, no. 2 (2016): 484-494. | ||

In article | View Article | ||

[8] | Zakernejad, Mohammad Hossein, Mohammad Mohammadi, and Mahdi Mehrtash. “A New Approach for Probabilistic Evaluation of Transient Recovery Voltage Across Circuit Breakers in TCSC Compensated Transmission Lines.” In Power System Conference (PSC), Tehran. 2014. | ||

In article | |||

[9] | Mehrtash, Mahdi, Masoud Jokar Kouhanjani, and Mohammad Mohammadi. “A new nonparametric density estimation for probabilistic security-constrained economic dispatch.” Journal of Intelligent & Fuzzy Systems Preprint: 1-12. | ||

In article | |||

[10] | Ferdowsi, Farzad, Ahmad Sadeghi Yazdankhah, and Homayoon Rohani. “A combinative method to control output power fluctuations of large grid-connected photovoltaic systems.” In Environment and Electrical Engineering (EEEIC), 2014 14th International Conference on, pp. 260-264. IEEE, 2014. | ||

In article | |||

[11] | Mehrtash, Mahdi, Mahdi Raoofat, Mohammad Mohammadi, Mohammad Hossein Zakernejad, and Hamidreza Zareipour. “Considering Multiple Uncertainties in Stochastic Security-Constrained Unit Commitment Using Point Estimation Method.” | ||

In article | |||

[12] | A. Sahba, John J. Prevost, “Hypercube based clusters in Cloud Computing”, presented at the 2016 World Automation Congress, Puerto Rico, USA, August 2016. | ||

In article | View Article PubMed | ||

[13] | A. Sahba, R. Sahba, and W.-M. Lin, “Improving IPC in Simultaneous Multi-Threading (SMT) Processors by Capping IQ Utilization According to Dispatched Memory Instructions”, presented at the 2014 World Automation Congress, Waikoloa Village, HI, August 2014. | ||

In article | View Article PubMed | ||

[14] | Ashkaboosi, Maryam, Seyed Mehdi Nourani, Peyman Khazaei, Morteza Dabbaghjamanesh, and Amirhossein Moeini. “An optimization technique based on profit of investment and market clearing in wind power systems.” American Journal of Electrical and Electronic Engineering 4, no. 3 (2016): 85-91. | ||

In article | |||

[15] | Ferdowsi, Farzad, Chris S. Edrington, and Touria El-mezyani. “Real-time stability assessment utilizing non-linear time series analysis.” In North American Power Symposium (NAPS), 2015, pp. 1-6. IEEE, 2015. | ||

In article | |||

[16] | Shiadeh, SeyyedMahdi Jafari, Mohammad Ardebili, and Parvin Moamaei. “Three-dimensional finite-element-model investigation of axial-flux PM BLDC machines with similar pole and slot combination for electric vehicles.” In Power and Energy Conference at Illinois (PECI), 2015 IEEE, pp. 1-4. IEEE, 2015. | ||

In article | |||

[17] | Bozorgi, Amir Masoud, Mohammad Monfared, and Habib Rajabi Mashhadi. “Optimum switching pattern of matrix converter space vector modulation.” In Computer and Knowledge Engineering (ICCKE), 2012 2nd International eConference on, pp. 89-93. IEEE, 2012. | ||

In article | View Article | ||

[18] | S Jafarishiadeh, M Ardebili, A Nazari Marashi, “Investigation of pole and slot numbers in axial-flux pm bldc motors with single-layer windings for electric vehicles,” 24th Iranian Conference on Electrical Engineering (ICEE), pp. 1444-1448, 2016. | ||

In article | View Article | ||

[19] | Seyyedmahdi Jafari Shiadeh, Mohammad Ardebili, and Parvin Moamaei, “Three-dimensional finite-element-model investigation of axial-flux PM BLDC machines with similar pole and slot combination for electric vehicles”, In: Proceedings of Power and Energy Conference, Illinois, pp. 1-4, 2015 | ||

In article | View Article | ||

[20] | A. Bozorgi, M. Farasat, and S. Jafarishiadeh, “Improved model predictive current control of permanent magnet synchronous machines with fauzzy based duty cycle control,” Energy Conversion Congress and Exposition (ECCE) 2016, in press. | ||

In article | |||

[21] | A. M. Bozorgi, M. Monfared, and H. R. Mashhadi, ”Two simple overmodulation algorithms for space modulated three-phase to three-phase matrix converter,” IET Power Electron., vol. 7, no. 7, pp. 1915-1924, Jul. 2014 | ||

In article | View Article | ||

[22] | S. M. Jafari-Shiadeh and M. Ardebili, “Analysis and comparison of axial-flux permanent-magnet brushless-DC machines with fractional-slot concentrated-windings”, Proc. 4th Annu. Int. Power Electron., Drive Syst., Technol. Conf., pp. 72-77, 2013. | ||

In article | View Article | ||

[23] | Khazaei, P., S. M. Modares, M. Dabbaghjamanesh, M. Almousa, and A. Moeini. “A high efficiency DC/DC boost converter for photovoltaic applications.” International Journal of Soft Computing and Engineering (IJSCE) 6, no. 2 (2016): 2231-2307. | ||

In article | |||

[24] | D. Ke and C. Y. Chung, “Design of Probabilistically-Robust Wide-Area Power System Stabilizers to Suppress Inter-Area Oscillations of Wind Integrated Power Systems,” in IEEE Transactions on Power Systems, vol. 31, no. 6, pp. 4297-4309, Nov. 2016. | ||

In article | View Article | ||

[25] | Ferdowsi, Farzad, Ahmad Sadeghi Yazdankhah, and Bahareh Abbasi. “Declining power fluctuation velocity in large PV systems by optimal battery selection.” In Environment and Electrical Engineering (EEEIC), 2012 11th International Conference on, pp. 983-988. IEEE, 2012. | ||

In article | |||

[26] | A. Sahba, Y. Zhang, M. Hays and W.-M. Lin, “A Real-Time Per-Thread IQ-Capping Technique for Simultaneous MultiThreading (SMT) Processors”, In the Proceedings of the 11th International Conference on Information Technology New Generation (lTNG 2014), April 2014. | ||

In article | PubMed | ||

[27] | Khazaei, Peyman, Morteza Dabbaghjamanesh, Ali Kalantarzadeh, and Hasan Mousavi. “Applying the modified TLBO algorithm to solve the unit commitment problem.” In World Automation Congress (WAC), 2016, pp. 1-6. IEEE, 2016. | ||

In article | View Article | ||

[28] | Ghaffari, Saeed, and Maryam Ashkaboosi. “Applying Hidden Markov Model Baby Cry Signal Recognition Based on Cybernetic Theory.” IJEIR 5, no. 3 (2016): 243-247. | ||

In article | |||

[29] | Ashkaboosi, Maryam, Farnoosh Ashkaboosi, and Seyed Mehdi Nourani. “The Interaction of Cybernetics and Contemporary Economic Graphic Art as” Interactive Graphics”.” (2016). | ||

In article | |||

[30] | Mehrtash, Mahdi, Masoud Jokar Kouhanjani, Amir Pourjafar, and Seyedbehnam Beladi. “An Interior Point Optimization Method for Stochastic Security-constrained Unit Commitment in the Presence of Plug-in Electric Vehicles.” Journal of Applied Sciences 16, no. 5 (2016): 189. | ||

In article | View Article | ||

[31] | M. Bagheri, M. Madani, R. Sahba, and A. Sahba, “Real time object detection using a novel adaptive color thresholding method”, International ACM workshop on Ubiquitous meta user interfaces (Ubi-MUI'11), Scottsdale, AZ, November 2011. | ||

In article | |||