A Model Predictive Control Method for Hybrid Energy Storage Systems

ABSTRACT:

The traditional PI controller for a hybrid energy storage system (HESS) has certain drawbacks, such as difficult tuning of the controller parameters and the additional filters to allocate high- and low- frequency power fluctuations. This paper proposes a model predictive control (MPC) method to control three-level bidirectional DC/DC converters for grid-connections to a HESS in a DC microgrid. First, the mathematical model of a HESS consisting of a battery and ultra capacitor (UC) is established and the neutral point voltage imbalance of a three level converter is solved by analyzing the operating modes of the converter. Secondly, for the control of the grid-connected converters, an MPC method is proposed for calculating steady state reference values in the outer layer and the dynamic rolling optimization in the inner layer. The outer layer ensures the voltage regulation and establishes the current predictive model, while the inner layer, using the model predictive current control, makes the current follow the predictive value, thus reducing the system current ripple. This cascaded topology has two independent controllers and is free of filters to realize the high-and low frequency power allocation for a HESS. Therefore, it allows two types of energy storage devices to independently regulate the voltage and realizes the power allocation of the battery and UC. Finally, simulation studies are conducted in PSCAD/EMTDC, and the effectiveness of the proposed HESS control strategy is verified in a case, such as a controller comparison and fault scenario.

KEYWORDS:

1.      Double layer control method

2.       Hybrid energy storage system (HESS)

3.      Model predictive control (MPC)

4.      Three-level DC/DC converter

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig. 1. The topology of a HESS.

EXPECTED SIMULATION RESULTS:

Fig. 2. Comparison under the proposed MPC method with the PI control method. (a) Bus voltage response under two methods. (b) UC voltage response under two methods.

 Fig. 3. The power response of the battery when the controller parameter _i is changed.

 Fig. 4. System voltage response in the case of short-circuiting of the UC.

(a) The response of the bus voltage during the short-circuit fault of the UC.

(b) The response of the UC voltage during the short-circuit fault of the UC.

Fig. 5. Photovoltaic module output power.

Fig. 6. Comparison between the proposed MPC method and the PI control method. (a) The bus voltage response under two methods. (b) The UC voltage response under two methods.

Fig. 7. The effectiveness under the proposed MPC method. (a) The voltage of capacitors C1 and C2. (b) Inductor L1 reference current iL1ref and actual current iL1.

 

CONCLUSION:

 In this paper, the advantages of a three-level bidirectional DC/DC converter for battery/UC HESS and the effectiveness of the proposed MPC method are discussed from both a theoretical analysis and simulation verification. At the same grid voltage level, the battery can suppress higher voltage level fluctuations after a two-stage boosting structure. Compared with the PI controller, the MPC controller doesn’t need a tedious step of adjusting parameters and various state variables are considered in each sampling instant. Moreover, the MPC algorithm based on the constant switching frequency achieves fast and accurate regulation of voltage and current with diminished ripples. Finally, the system does not need filters to allocate power fluctuations, and the control structure is optimized while the battery life is prolonged.

REFERENCES:

[1] D. Liang, C. Y. Qin, S. Y. Wang, and H. M. Guo, “Reliability evaluation of DC distribution power network,” in Proceedings of 2018 China International Conference on Electricity Distribution, Tianjin, 2018, pp. 654–658.

[2] Z. Huang, J. Ma, J. Zeng et al., “Research status and prospect of control and protection technology for DC distribution network,” in Proceedings of 2014 China International Conference on Electricity Distribution, Shenzhen, Sep. 2014, pp. 1488–1493.

[3] K. A. Joshi and N. M. Pindoriya, “Case-specificity and its implications in distribution network analysis with increasing penetration of photovoltaic generation,” CSEE Journal of Power and Energy Systems, vol. 3, no. 1, pp. 101–113, Mar. 2017.

[4] Y. Xu, T. Y. Zhao, S. Q. Zhao, J. H. Zhang, and Y. Wang, “Multiobjective chance-constrained optimal day-ahead scheduling considering BESS degradation,” CSEE Journal of Power and Energy Systems, vol. 4, no. 3, pp. 316–325, Sep. 2018.

[5] Y. Sun, Z. Zhao, M. Yang, D. Jia, W. Pei and B. Xu, “Overview of energy storage in renewable energy power fluctuation mitigation,” CSEE Journal of Power and Energy Systems, vol. 6, no. 1, pp. 160–173, Mar. 2020.

A Lyapunov-Function Based Controller for 3-Phase Shunt Active Power Filter and Performance Assessment Considering Different System Scenarios

 

ABSTRACT:

Shunt active power filter (SAPF) belongs to the class of custom power devices (CPDs) and offers compensation to harmonics originated owing to customer side nonlinear loads, reactive power and unbalance in the distribution power networks functioning in current control mode (CCM). The performance of a SAPF as a harmonic compensator entirely relies on the control technique i.e. the precise detection of the harmonic current components of load that are necessary to be compensated. In the present work, a 3-phase SAPF, inspired by a Lyapunov function based control approach, has been designed for compensation of harmonics resulted in the feeder current owing to the customer side nonlinearity. A control law is determined in the proposed strategy which makes the derivative of the Lyapunov function consistently a negative one for an entire set of stable states. The DC-link capacitor voltage is regulated at constant reference through the proportional-integral (PI) controller. In this method rating of the shunt active power filter is considerably reduced than the other two broadly employed conventional methods. Furthermore, the harmonic compensation efficacy of the proposed Lyapunov function based SAPF is compared with the one based on other two conventional approaches under four different system scenarios namely a simple nonlinear load with and without utility side voltage distortion, a modified IEEE 13 bus test distribution system loaded with a 3-phase chopper fed direct current (DC) motor drive at a single bus and last especially for increasing the harmonic-constrained penetration level of renewable energy. Results obtained through simulation performed in MATLAB/Simulink shows that total harmonic distortion (THD) of source current and dynamic, as well as steady-state performance with Lyapunov function based controller, is significantly improved than the other two conventional methods. Also, the robust compensation performance of the SAPF empowers it to deal with the high penetration of renewable energy.

KEYWORDS:

1.      SAPF

2.      Lyapunov function

3.      Harmonic compensation

4.       Hysteresis controller

5.      Renewable energy

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Figure 1. Configuration Of Sapf.

EXPECTED SIMULATION RESULTS:

Figure 2. Waveforms Of Lyapunov Function Based Control Technique (A-B) Before And (C-E) After Compensation.

Figure 3. Fft Analysis A) Before Compensation, B) After Compensation.

 

Figure 4. Dynamic Performance Of Sapf Using P-Q Theory With An Unbalanced Or Distorted Source Voltage.

 

 Figure 4. (Continued.) Dynamic Performance Of Sapf Using P-Q Theory With An Unbalanced Or Distorted Source Voltage.

Figure 5. Dynamic Performance Of Sapf Using Srf Theory With An Unbalanced Or Distorted Source Voltage.

 Figure 5. (Continued.) Dynamic Performance Of Sapf Using Srf Theory With An Unbalanced Or Distorted Source Voltage.

 

CONCLUSION:

A control algorithm, based on the Lyapunov function, is proposed for SAPF to mitigate harmonics and reactive power compensation of nonlinear loads. The performance of SAPF has been found satisfactory under all four cases of the study. The control algorithm is established on the Lyapunov function for achieving global stability in the system. The simulation results validate the control approach for SAPF. A hysteresis controller has been used to generate a switching signal for the voltage source inverter. Based on simulation results following conclusions have been drawn.

1) All the control algorithm's (p-q theory, SRF theory, Lyapunov function based control theory) performance found satisfactory i.e. THD is less than 5% according to IEEE 519 standards.

2) Under the fully fundamental plus balanced source voltage and purely nonlinear loading condition Lyapunov function-based control algorithm gives the best performance over the other two control algorithms which are commonly used.

3) The THD of the source current under the Lyapunov function based control algorithm is 1.61% in phase a, 2.33% in phase b, 1.99% in phase c when applied on a two-bus system under purely nonlinear load. In the case of a modified 13-bus system, the same with Lyapunov function based control algorithm is 1.59% in phase a, 1.61% in phase b, 1.52% in phase c.

4) In case of distortion and unbalance present in the utility's voltage, the detection of the reference current is accurately performed by the Lyapunov function-based control algorithm and superiorly in contract to the other two control algorithms.

5) It is also inferred that the dynamic response of the system with the Lyapunov function-based control algorithm to be better than the other two control algorithms.

6) Last but not the least, the harmonic and reactive power compensation offered by Lyapunov function-based SAPF is better also in the case of renewable energy's penetration. The proposed theory-based SAPF has the potential of enhancing the penetration level of HC-HC of the modern and polluted DPS up to more extent.

REFERENCES:

[1] X. Zong, P. A. Gray, and P. W. Lehn, ``New metric recommended for IEEE standard 1547 to limit harmonics injected into distorted grids,'' IEEE Trans. Power Del., vol. 31, no. 3, pp. 963_972, Jun. 2016.

[2] O. F. Kececioglu, H. Acikgoz, C. Yildiz, A. Gani, and M. Sekkeli, ``Power quality improvement using hybrid passive _lter con_guration for wind energy systems,'' J. Electr. Eng. Technol., vol. 12, no. 1, pp. 207_216, Jan. 2017.

[3] G. K. Singh, ``Power system harmonics research: A survey,'' Eur. Trans. Electr. Power, vol. 19, no. 2, pp. 151_172, Mar. 2009.

[4] S. S. Reddy and P. R. Bijwe, ``Real time economic dispatch considering renewable energy resources,'' Renew. Energy, vol. 83, pp. 1215_1226, Nov. 2015.

[5] IEEE Recommended Practice and Requirements for Harmonic Control in Electric Power Systems, IEEE Std 519-2014 (Revision IEEE Std 519- 1992), Nov. 2014, pp. 1_29.

A Common Capacitor Based Three Level STATCOM and Design of DFIG Converter for a Zero-Voltage Fault Ride-Through Capability

 

ABSTRACT:

To meet the augmented load power demand, the doubly-fed induction generator (DFIG) based wind electrical power conversion system (WECS) is a better alternative. Further, to enhance the power flow capability and raise security margin in the power system, the STATCOM type FACTS devices can be adopted as an external reactive power source. In this paper, a three-level STATCOM coordinates the system with its dc terminal voltage is connected to the common back-to-back converters. Hence, a lookup table-based control scheme in the outer control loops is adopted in the Rotor Side Converter (RSC) and the grid side converter (GSC) of DFIG to improve power flow transfer and better dynamic as well as transient stability. Moreover, the DC capacitor bank of the STATCOM and DFIG converters connected to a common dc point. The main objectives of the work are to improve voltage mitigation, operation of DFIG during symmetrical and asymmetrical faults, and limit surge currents. The DFIG parameters like winding currents, torque, rotor speed are examined at 50%, 80% and 100% comparing with earlier works. Further, we studied the DFIG system performance at 30%, 60%, and 80% symmetrical voltage dip. Zero-voltage fault ride through is investigated with proposed technique under symmetrical and asymmetrical LG fault for super-synchronous (1.2 p.u.) speed and sub-synchronous (0.8 p.u.) rotor speed. Finally, the DFIG system performance is studied with different phases to ground faults with and without a three-level STATCOM.

KEYWORDS:

1.      Doubly-fed induction generator (DFIG)

2.      Field oriented control (FOC)

3.      Common-capacitor based STATCOM

4.      Voltage compensation

5.      Balanced and unbalanced faults

6.      Zero-voltage fault ride through

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Figure 1. Grid-Connected DFIG With Three Levels Statcom Converter.

 EXPECTED SIMULATION RESULTS:

Figure 2. DFIG Operation With 50% Voltage Dip (I) Using Method In [27]. And (Ii) Using Proposed Method.

Figure 3. DFIG Operation With 50% Voltage Dip (I) Using Method In [28] And (Ii) Using Proposed Method.

 Figure 4. DFIG Operation With (I) 30% Dip, (Ii) 60% Dip And (Iii) 80% Dip In Grid Voltage.

 Figure 5. Rotor, Stator Gsc And Grid Terminal Current Waveforms With The Proposed Technique With Slg Fault. 

CONCLUSION:

 A generalized DFIG wind energy conversion system based test-bed system connected to the grid is considered in the paper. The work tested in the starting cases with two different research papers works with proposed method under an 80% dip. Later, proposed methodology compared under 30%, 60%, and 80% dip, and the DFIG behavior is examined. Further, under three different cases, LG, LLG and LLG faults without and STATCOM are compared to show STATCOM controller's effectiveness. An improved field-oriented control scheme for the DFIG with real and reactive power lookup-based control in the outer control loops. It is observed that, there is a rapid development in the back emf and decoupled current regime in the paper's inner control loops is proposed. A three-level SATCOM is used in this paper, with the rectifier end dc-link connected to the common capacitor between the DFIG back-to-back converters. A better damping factor is observed for torque, powers, current, voltage, and speed at 60%, 80%, and 100% dip with the proposed scheme.

The proposed method employs the adjustment of external real and reactive powers using the optimal lookup table method as shown in Table 3, rotor speed, and terminal voltage in the outer control loops of both RSC and GSC. The inner control loop is fast-acting current control and back emf- based voltage injection near the decoupling voltage loop. The strategy works on decoupled real and reactive power flow controls in synchronous rotating frames leads to individual power control. This technique improves performance under normal conditions and during grid faults, with better rotor voltage control, rotor speed, and damping. The post-fault behavior of an overall system improved using the proposed technique.

Further improvement in the system behavior is observed with the common- dc link STATCOM. The rectifier end dc link is connected to the capacitor between the DFIG converters, which will reduce the cost for capacitor and measurement sensors. This paper demonstrates the DFIG-based WECS with better active and reactive power and EMT damping, surge current reduction, speed control, and effective LVRT capability. There are distortions in the rotor current waveform during the zero-voltage fault ride during the fault and considerably more when the rotor speed is at super synchronous speed. When the rotor speed is beyond the synchronous speed, the rotor current is injected into the stator terminal from the rotor side windings with RSC control scheme. Under this condition, the fault inrush current from the dc-link capacitor will pass through this rotor terminal and reach the stator windings. Under sub-synchronous speed, the rotor winding will receive the current for the stator windings, so the fault effect is less influenced at lower speeds than with higher speeds. The rotor voltage is maintained at both speeds during the LG fault. However, waveform is less distorted with lower rotor speed.

The dc-link voltage distortions during the fault are more with super- synchronous speed than sub-synchronous speed operation for zero voltage ride through. The dc-link voltage is more stubborn and stable when the rotor speed is lesser than the synchronous speed. The STATCOM current is observed to be more in faulty phase than with other two healthy phases. The reason and analysis are the same as that with the symmetrical fault study. The deviation of the fault current at the STATCOM terminal is re-injected to the grid via the closed path with the dc-link capacitor terminal. The post-fault performance is superior with a serious 100% voltage dip case and also found better dynamic response because of the RSC and GSC proposed technique and the STATCOM controller. Further, an effective operation is experienced with a common link dc capacitor STATCOM than with a conventional topology. Hence, simulated results show better performance and profitable operation during and after the faults than the earlier famous methods.

With the proposed method, rotor and stator current during fault are maintained, not getting zero value and limiting surge currents to a dangerous value. However, stator and rotor current is not supported to their pre-fault value during the fault period. The torque reduction to a smaller value observed increases the grid fault dip value, but there are no surges and oscillations with the proposed method. The rotor speed is also maintained almost constant even for significant voltage dip. As a result, the post fault recovery in the DFIG is smooth and instantaneous, observed for winding voltages, currents, EMT, active and reactive powers, dc-link capacitor voltage, and rotor speed.

All the objectives specified in the Introduction section are met 1) rotor and stator current surges are limited, current surges ate within 1.5 times the operating value, mitigation in the rotor voltage observed. Furthermore, the reactive power support by STATCOM, RSC and GSC improved the DFIG WECS during and after the fault. Thereby 1) enhancement in overall dynamic and transient stability is observed. 2) The rotor speed is almost constant even for a significant grid voltage dip which is better than many research papers. 3) The electromagnetic torque (EMT) and active and reactive power flow oscillations are damped completely, and sustainable control observed with the technique. 4) The proposed method is suitable for grid faults like symmetrical, asymmetrical, and recurring faults. Better DFIG performance is expected with LVRT capability for symmetrical and asymmetrical faults with future research activities.

REFERENCES:

[1] H. A. Mohammadpour, A. Ghaderi, H. Mohammadpour, and E. Santi, ``SSR damping in wind farms using observed-state feedback control of DFIG converters,'' Electr. Power Syst. Res., vol. 123, pp. 57_66, Jun. 2015.

[2] F. Blaabjerg and K. Ma, ``Future on power electronics for wind turbine systems,'' IEEE J. Emerg. Sel. Topics Power Electron., vol. 1, no. 3, pp. 139_152, Sep. 2013.

[3] T. D. Vrionis, X. I. Koutiva, and N. A. Vovos, ``A genetic algorithm based low voltage ride-through control strategy for grid connected doubly fed induction wind generators,'' IEEE Trans. Power Syst., vol. 29, no. 3, pp. 1325_1334, May 2014.

[4] A. M. Eltamaly and H. M. Farh, ``Maximum power extraction from wind energy system based on fuzzy logic control,'' Electr. Power Syst. Res., vol. 97, pp. 144_150, Apr. 2013.

[5] Y. Weng and Y. Hsu, ``Sliding mode regulator for maximum power tracking and copper loss minimisation of a doubly fed induction generator,'' IET Renew. Power Gener., vol. 9, no. 4, pp. 297_305, May 2015.

Modeling and Simulation of Impedance Distance Relay for Fault Location and Protection of Single Wire Earth Return Line

ABSTRACT:

Different technologies and resources are utilized to provide electricity access for the rural population around the world. Single wire earth return (SWER) line gets prominent attention around the globe to electrify low load profile customers and remote load like telecom base stations by extending from the nearby medium grid. SWER distribution system is designed by tapping from medium voltage distribution line using an isolation transformer. Unlike other distribution systems, the secondary side of a transformer has an only single line with dedicated perfect grounding system. SWER lines are considered as a cost-effective solution, compared to the three phase grid extension by electric utility companies. Since line route is mostly in rural areas with different geographical topologies, natural and human-made faults are inevitable scenarios on the line. According to a preference of utilities and geographical locations, SWER lines are equipped with over current relay, surge arrestors or reclosers to isolate faulty line during the fault. The two main challenges on SWER line protection are to back up existing over current protection relay when it fails to clear the fault and to locate the location of fault for line maintenance. Technicians patrol up to hundreds of km along SWER line to locate a fault. This activity will be inefficient and time-consuming way of locating the fault. In this paper, we model and simulate the impedance distance relay to back up existing protection system and locate the fault. Our model successfully backs up definite time over current (DTOC) relay for a single line to ground (SLG) faults across the line. Consequently, fault locator-block locates the faulty line position.

 KEYWORDS:

1.      SWER

2.      Rural Electrification

3.      Impedance relay

4.      Fault location

5.      Protection

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

 Fig.1.Impedance relay simulation model

 EXPECTED SIMULATION RESULTS:

 

Fig.2.Fault cleared by DTOC

 Fig.3.Fault cleared by Zone-1 relay

 

Fig.4.Fault cleared by zone -2 relay

 

CONCLUSION:

In this paper, the two challenges on SWER line, backup protection of DTOC relay and fault location during fault are addressed. An impedance relay is proposed to backup DTOC relay and to locate faults on SWER line.The simulation is done on MATLAB/SIMULINK on each step of 15km from relay point to the entire line. A fault is simulated at 0.4 s and during the inception of fault, the proposed impedance relay managed to clear the fault according to the intentional time delay set between each zone when DTOC fails to operate. Fault locator-block also measures the fault location by considering fault impedance during a fault. The model can measure a SWER line fault location for a fault impendence of 5Ω and below with less than 3% errors. Whereas, fault impedance compensation is required for a fault impedance greater than 10Ω to achieve better result with minimum error percentage.

 REFERENCES:

[1] P. Cook, "Infrastructure, rural electrification and development," Energy Sustinable Development , pp. 304-313, 2011.

[2] IEA, "Iea.org/sdg/electricity/," IEA, [Online]. Available: https://www.iea.org/sdg/electricity/. [Accessed 10 03 2019].

[3] ESAMP, "Reducing the Cost of Grid Extension for Rural Electrifcation," The International Bank for Reconstruction and Development 227.200, USA, 2000.

[4] L.MANDENO, "RURAL POWER SUPPLY, ESPECIALLY IN BACK COUNTRY AREAS.," in Proceedings of the New Zealand Institution of Engineers, Vol. 33 (1947), 1947.

[5] P. Grad, "Energy Source & Distribution," 2014, 18 May 2014. Available: https://www.esdnews.com.au/swer-still-going-strong/. [Online] [Accessed 11 March 2019].

Transmission Line Protection with Distance Relay

                      

ABSTRACT:

 With the development in science and engineering the power system protection field also get advanced which includes the development of relays .the relays journey started by electromechanical then solid state and now digital and numerical relays .An economical and feasible solution to investigate the performance of relays and protection system offered by modeling of protective relays .Distance relay is one of the effective protective relays that are used for the protection of extra high voltage transmission lines. Distance relays are considered of the high speed class and can provide protection. To detect the fault on transmission lines many distance relays are used but for long transmission line mho relay is most suited. The proposed work is about designing of numerical mho relay in MATLAB / SIMULINK to be used for distance protection schemes of long distance transmission lines with better result and characteristics. The required mho relay algorithm is evaluated by using MATLAB to model the power system under different fault condition and simulate it by using phasor based method available in MATLAB simulation. Thus the modeling and simulation of numerical mho relay gives the improved result and greatly enhance the performance of mho relay

KEYWORDS:

1.      Distance protection

2.      Numerical relays

3.      Matlab/Simulink

SOFTWARE: MATLAB/SIMULINK 

BLOCK DIAGRAM:

                                     
EXPECTED  SIMULATION RESULTS:

 

CONCLUSION:

 This work presents a detailed phasor model for a distance relay of mho characteristics. Mho relays are inherently directional so there is no need for directional elements in the relay model. Here the developed simulation is evaluated for line to line fault on the system, and the results found as Simulation results of different faults regarding type and position show clearly the accurate performance of the developed distance relay model. From results it is seen that speed of operation of numerical mho relay is faster than impedance relay. The model versatility, adaptability and applicability promote it for use in power system simulators. Also, it can be used as a training tool to help users understand how a distance relay works and how settings are performed.

REFERENCES:

I. P.G. Mclaren SM, G.W. Swift SM, 2. Zhang, E. Dirks, R.P. Jayasinghe, I. Fernandouniversity Of Manitoba, Winnipeg, Manitoba, Canada, R3T 2N2.” A New Directional Element For Numerical Distance Relays” IEEE Transactions On Power Delivery, Vol. 10, No. 2, April 1995.

II. P. G. Mclaren, K. Mustaphi, G. Benmouyal, S. Chano, A. Girgis, C. Henville, M. Kezunovic, L. Kojovic, R. Marttila, M. Meisinger, G. Michel, M. S. Sachdev, V. Skendzic, T. S. Sidhu, And D. Tziouvaras” Software Models For Relays” IEEE Transactions On  Power Delivery, VOL. 16, NO. 2, APRIL 2001.

III. Shailendra Kumar Saroj, Harish Balaga, D. N. Viswakarma (Banaras Hindu University), Varanasi, India ” Discrete Wavelet Transform Based Numerical Protection Of Transmission Line ”, Department Of Electrical Engineering Indian Institute Of Technology

IV. Li-Cheng Wu, Chih-Wen Liu, Ching-Shan Chen,Member, National Taiwan University, Taipei, Taiwa, “Modeling And Testing Ofa Digital Distance Relay Using MATLAB / SIMULINK ,IEEE Transaction On Power Delivery,2005.

V. Eng. Abdlmnam A. Abdlrahem , Dr.Hamid H Sherwali Modelling Of Numerical Distance Relays Using Matlab ”, “IEEE Symposium On Industrial Electronics And Applications”,Octobe,2009.