Dynamic Modular Modeling of Smart Loads Associated with Electric Springs and Control

ABSTRACT:  

Smart loads associated with electric springs (ES) have been used for fast demand-side management for smart grid. While simplified dynamic ES models have been used for power system simulation, these models do not include the dynamics of the power electronic circuits and control of the ES. This paper presents a dynamic and modular ES model that can incorporate controller design and the dynamics of the power electronic circuits. Based on experimental measurements, the order of this dynamic model has been reduced so that the model suits both circuit and system simulations. The model is demonstrated with the radial chordal decomposition controller for both voltage and frequency regulation. The modular approach allows the circuit and controller of the ES model and the load module to be combined in the d-q frame. Experimental results based on single and multiple smart loads setup are provided to verify the results obtained from the model simulation. Then the ES model is incorporated into power system simulations including an IEEE 13 node power system and a three-phase balanced microgrid system.

KEYWORDS:

1.      Electric spring

2.      Parameter estimation

3.      Radial-chordal decomposition

4.      Smart loads

5.      Microgrids

SOFTWARE: MATLAB/SIMULINK

SCHEMATIC DIAGRAM:

Fig. 1 System setup in Phase III.

 EXPECTED SIMULATION RESULTS:

(a)Full results of experiment and the theoretical model.

(b)Zoom in results of experiment and the theoretical model.

(c) Full results of experiment and the estimated model.

(d) Zoom in results of experiment and the estimated model.

Fig. 2 Experimental and simulation (theoretical and estimated models) results of ES output voltage.

(a) PCC Voltage (V_g).

(b) Voltage output of ES (V_es).

(c) Current of the Smart load (I_sl).

(d) P-Q power of the smart load.

Fig. 3 Experimental and simulation results on Phase II setup with a ZIP load.

(a) PCC Voltage (V_g).

(b) Voltage output of ES (V_es).

411

(c) Current of the Smart load (I_sl).

(d) P-Q power of the smart load.

Fig. 4 Simulation results on Phase II setup with a thermostatic load.

(a) PCC voltage (V_g1/2/3).

 

(b)Voltage output of ES 1 (V_es1).

(c) Voltage output of ES 2 (V_es2).

(d) Voltage output of ES 3 (V_es3).

(e) P-Q power of smart load 1.

(f) P-Q power of smart load 2.

(g) P-Q power of smart load 3.

Fig. 5 Experimental and simulation results on Phase III setup.

(a) Power delivered by the renewable energy source.

(b)Phase A voltage of node 634 (V_s).

(c) Power absorbed in phase A of node 634.

(d)Sum power absorbed by smart load 1,2 and 3.

(e) Power absorbed by smart load 4.

(f) Power absorbed by smart load 5.

Fig. 6 Simulation results on Phase IV setup.

(a) Utility frequency

(b) PCC voltage (V_g)

Fig. 7 Simulation results on Phase V setup.

CONCLUSION:

In this paper, the dynamic model of an ES is firstly analyzed as a theoretical model in state space. An order-reduced model is derived by estimation based on experimental measurements. A theoretical model of the order of 6 with 4 inputs has been simplified into a 2nd-order model with 2 inputs. The RCD control is adopted as the outer-controller module in the smart load. Two models of noncritical loads, namely ZIP and thermostatic load models, are analyzed to cooperate with the ES. The estimated ES model (the inner model), outer controller and the load model can be modelled separated as modules and then combined to form the smart load model. The modular approach offers the flexibility of the proposed model in outer-controller design and the noncritical load selection. The results obtained from the proposed model are compared with experimental measurements in different setups for model verification. The proposed model has been tested for voltage and frequency regulation. This simplified modular modeling method could pave the way for future work on modeling widely-distributed ESs in distribution networks so that various control strategies can be studied.

REFERENCES:

[1] J.M. Guerrero, J.C. Vasquez, J. Matas, M. Castilla and L. Garcia de Vicuna, “Control strategy for flexible microgrid based on parallel line-interactive UPS systems”, IEEE Transaction on Industrial Electronics, vol. 56, no.3, pp. 726-735, Mar. 2009.

[2] P. Khayyer and U. Ozguner, “Decentralized control of large-scale storage-based renewable energy systems”, IEEE Transactions on Smart Grid, vol. 5, no.3, pp. 1300-1307, May 2014.

[3] Yang, Y., H. Wang, F. Blaabjerg, and T. Kerekes. “A Hybrid Power Control Concept for PV Inverters With Reduced Thermal Loading.” IEEE Transaction on Power Electronics, vol 29, no. 12, pp. 6271– 6275, Dec. 2014.

[4] A. H. Mohsenian-Rad, V. W. S. Wong, J. Jatskevich, R. Schober, and A. Leon-Garcia, “Autonomous demand-side management based on game-theoretic energy consumption scheduling for the future smart grid,” IEEE Transaction Smart Grid, vol. 1, no. 3, pp. 320– 331, Dec. 2010.

[5] A. J. Conejo, J. M. Morales and L. Baringo, “Real-time demand response model,” IEEE Trans. Smart Grid, vol. 1, no. 3, pp. 236–242, Dec. 2010.

Enhancement of Voltage Stability and Power Oscillation Damping Using Static Synchronous Series Compensator with SMES

 ABSTRACT:  

 The power system network is becoming more complex nowadays and it is very difficult to maintain the stability of the power system. The main purpose of this paper proposes a 12-pulse based Static Synchronous Series Compensator (SSSC) with and without Superconducting Magnetic Energy Storage (SMES) for enhancing the voltage stability and power oscillation damping in multi area system. Control scheme for the chopper circuit of SMES coil is designed. A three area system is taken as test system and the operation of SSSC with and without SMES is analysed for various transient disturbances in MATLAB / SIMULINK environment.

KEYWORDS:

1.      Static Synchronous Series Compensator (SSSC)

2.      Superconducting Magnetic Energy Storage (SMES)

3.      Multi area system

4.      Transient disturbances

SOFTWARE: MATLAB/SIMULINK

SINGLE LINE DIAGRAM:

Fig. 1 Single line diagram of the test system with SSSC with SMES

 EXPECTED SIMULATION RESULTS:

Fig. 2.Simulation result of test system

Fig. 3 Power output for Case (a) and (b)

(a) With fault

(b) Case (a)

(c) Case (b)                     Time (sec)

Fig. 4 Simulation result of Voltage with fault

Fig. 5 Simulation result for current with fault

Fig, 6 Simulation result for P & Q with fault

CONCLUSION:

The dynamic performance of the SSSC with and without SMES for the test system are analysed with Matlab/simulink. In this paper SMES with two quadrant chopper control plays an important role in real power exchange. SSSC with and without has been developed to improve transient stability performance of the power system. It is inferred from the results that the SSSC with SMES is very efficient in transient stability enhancement and effective in damping power oscillations and to maintain power flow through transmission lines after the disturbances.

REFERENCES:

[1] S. S. Choi, F. Jiang and G. Shrestha, “Suppression of transmission system oscillations by thyristor controlled series compensation”, IEE Proc., Vol.GTD-143, No.1, 1996, pp 7-12.

[2] M.W. Tsang and D. Sutanto, “Power System Stabiliser using Energy Storage”, 0-7803-5935-6/00 2000, IEEE

[3] Hingorani, N.G., “Role of FACTS in a Deregulated Market,” Proc. IEEE Power Engineering Society Winter Meeting, Seattle, WA, USA, 2006, pp. 1-6.

[4] Molina, M.G. and P. E. Mercado, “Modeling of a Static Synchronous Compensator with Superconducting Magnetic Energy Storage for Applications on Frequency Control”, Proc. VIII SEPOPE, Brasilia, Brazil, 2002, pp. 17-22.

[5] Molina, M.G. and P. E. Mercado, “New Energy Storage Devices for Applications on Frequency Control of the Power System using FACTS Controllers,” Proc. X ERLAC, Iguazú, Argentina, 14.6, 2003, 1-6.

A New Protection Scheme for HVDC Converters against DC Side Faults with Current Suppression Capability

 ABSTRACT:  

Voltage-source converters (VSCs) and half bridge Modular Multilevel Converters (MMCs) are among the most popular types of HVDC converters. One of their serious drawbacks is their vulnerable nature to DC side faults, since the freewheeling diodes act as a rectifier bridge and feed the DC faults. The severity of DC side faults can be limited by connecting double thyristor switches across the semiconductor devices. By turning them on, the AC current contribution into the DC side is eliminated and the DC-link current will freely decay to zero. The main disadvantages of this method are: high dv/dt stresses across thyrsitors during normal conditions, and absence of bypassing for the freewheeling diodes during DC faults as they are sharing the fault current with thyristors. This paper proposes a new protection scheme for HVDC converters (VSCs as well as MMCs). In this scheme, the double thyristor switches are combined and connected across the AC output terminals of the HVDC converter. The proposed scheme provides advantages such as lower dv/dt stresses and lower voltage rating of thyristor switches, in addition to providing full separation between the converter semiconductor devices and AC grid during DC side faults. A simulation case study has been carried out to demonstrate the effectiveness of the proposed scheme.

KEYWORDS:

1.      DC side faults

2.      Double Thyristor Switch

3.      Fault current suppression

4.      Protection of VSC-HVDC

5.      Protection of MMC-HVDC

SOFTWARE: MATLAB/SIMULINK

SCHEMATIC DIAGRAM:

Fig. 1. Description of simulated case study

 EXPECTED SIMULATION RESULTS:

Fig. 2. Simulation results for VSC case: (a) converter line voltage , (b) per-phase grid current, (c) DC-link current, (d) thyristors currents for different protection schemes, (e) freewheeling diode current for different protection scheme, and (f) dv/dt stresses across each thyristor for different protection schemes.

Fig. 3. Simulation results for three-level MMC (n=2): (a) converter line voltage , (b) per-phase grid current, (c) DC-link current, (d) thyristors currents for different protection schemes, (e) freewheeling diode current for different protection scheme, and (f) dv/dt stresses across each thyristor for different protection schemes.

CONCLUSION:

Depending on AC circuit breakers (ACCBs) to protect HVDC converters against DC side faults is a risk since the full AC fault current is passing through the freewheeling diodes until tripping the ACCBs is achieved. Hence, the need for complex DC breakers has emerged as the alternative. In this paper, a protection scheme for both VSC-HVDC and MMCHVDC converters against DC side faults is proposed. The proposed scheme provides complete separation between the AC side and the HVDC converters during DC faults which allows the DC-link current to freely decay to zero (the grid current contribution into DC fault is eliminated). A comparison between the proposed scheme and other existing schemes (STSS, and DTSS) is presented. With the same number of thyristors, the proposed scheme is able to accomplish the task of the DTSS, but with back-to-back thyristor switches exposed to lower dv/dt stresses, and possessing lower voltage (33% compared to other schemes), but higher current rating (200% compared to other schemes). Implementation of the proposed scheme is less complex since it is connected across the AC terminals of the converter not across semiconductor devices as in the single and double thyristor switch schemes.

REFERENCES:

[1] N. Flourentzou, V.G. Agelidis, G.D. Demetriades, "VSC-Based HVDC Power Transmission Systems: An Overview", IEEE Transactions on Power Electronics ,Vol. 24 , No. 3, pp. 592 - 602, March 2009.

[2] P. Lundberg,M. Callavik, M. Bahrman, P. Sandeberg, "High-Voltage DC Converters and Cable Technologies for Offshore Renewable Integration and DC Grid Expansions" IEEE Power and Energy Magazine, Vol. 10 , No. 6 , pp. 30-38, Nov. 2012.

[3] Lidong Zhang et al. “Interconnection of two very weak ac systems by VSC-HVDC links using power-synchronization control”, IEEE Trans. on Power Systems, vol. 26 , no. 1, pp.344-355, 2011.

[4] J. M. Espi, J.Castello, “Wind turbine generation system with optimized dc-link design and control”, IEEE Trans. on Ind. Electron. , vol. 60, no.3, pp. 919- 929, 2013.

[5] S. Cole, R. Belmans, “Transmission of bulk power”, IEEE Ind. Electron. Magazine, vol. 3, no.3, pp.19-24, Sept. 2009.