Evaluation of Battery System for Frequency Control in Interconnected Power System with a Large Penetration of Wind Power Generation

ABSTRACT:

Recently, a lot of distributed generations such as wind power generation are going to be installed into power systems. However, the fluctuation of these generator outputs affects the system frequency. Therefore, introduction of battery system to the power system has been considered in order to suppress the fluctuation of the total power output of the distributed generation. For frequency analysis, we use the interconnected 2-area power system model. It is assumed that a small control area with a large penetration of wind power plants is interconnected into a large control area. In this system, the tie line power fluctuation is very large as well as the system frequency fluctuation. It is shown that the installed battery can suppress these fluctuations and that the effect of battery on suppression of fluctuations depends on the battery capacity. Then, the required battery capacity for suppressing the tie line power deviation within a given level is calculated.

KEYWORDS:

1.      Battery

2.       Distributed Generation

3.      Frequency

4.      Load Frequency Control (LFC)

5.      Power System

6.      Tie Line Power

7.      Wind Power Generation

SOFTWARE: MATLAB/SIMULINK

2-AREA POWER SYSTEM:

Fig. 1. 2-area power system model for frequency control.

EXPECTED SIMULATION RESULTS:

Fig.2. Impact of LFC control method.

Fig. 3. Behaviors of tie line power flow, system frequency and battery

output with/without battery (Kb = 0.5, Tb = 0.5).

Fig. 4 Behaviors of tie line power and output and stored energy of battery

(9OMWh, 1500MW)

CONCLUSION:

In this paper, we have analyzed the impact of installed wind power generation and battery on the system frequency and the tie line power. In 2-area power systems, the tie line power fluctuation is remarkably large as well as the system frequency fluctuation. It has been made clear that the installed battery can suppress these fluctuations and that the effect of battery on suppression of these fluctuations depends on battery capacity. If the stored energy of battery reaches the full capacity, the battery output changes to zero suddenly and the large fluctuation is caused. Therefore, the stored energy    needs to be controlled within the rated storage capacity Based on this need, the required battery capacity for suppressing the tie line power deviation within a reference level has been calculated. If battery and LFC generator are controlled cooperatively, installation of battery with a larger capacity makes it possible to decrease LFC capacity of the conventional generators.  In the near future, a new method to calculate the optimal  battery storage capacity (MWh) and the appropriate power converter capacity (MW) for various kinds of wind power generation patterns and an effective control method of the battery system for reducing the battery capacity and LFC capability of the conventional power plants will be studied.

REFERENCES:

[1] W. El-Khattam and M. M. A. Salama, "Distributed generation technologies, definitions and benefits," Electric Power Systems  Research, vol. 71, issue 2, pp. 1 19-128, Oct. 2004.

[2] N. Jaleeli, L. S. VanSlyck, D. N. Ewart, L. H. Fink, and A. G. Hoffmann, "Understanding automatic generation control," IEEE Trans. Power Syst., vol. 7, pp. 1106-1122, Aug. 1992.

[3] A. Murakami, A. Yokoyama, and Y. Tada, "Basic study on battery capacity evaluation for load frequency control (LFC) in power system  with a large penetration of wind power generation," T. IEE Japan, vol. 126-B, no. 2, pp. 236-242, Feb. 2006. (in Japanese)

[4] P. Kunder, "Power System Stability and Control, " McGraw-Hill, 1994.

[5] A. J. Wood and B. F. Wollenberg, "Power Generation Operation and  Control," 2nd ed., Wiley, New York, 1966.

Shunt Isolated Active Power Filter With Common DC Link Integrating Braking Energy Recovery in Urban Rail Transit

 ABSTRACT:

In urban rail transit, there is a large number of harmonics brought by diode rectifiers, and shunt

active power filters (APFs) are an effective method of harmonics rejection. Traditional shunt APFs work with a dedicated DC link leading to complexity, while those with a common DC bus but using non-isolated topologies bring serious problems of zero-sequence circulating current (ZSCC), which introduce losses and provoke poor quality. Consequently, this paper first analyzes the limitations of traditional non-isolated APFs on modulation radio. Based on the analysis, this paper put forward a novel isolated APF with a common DC link based on existing diode rectifiers in urban rail transit, which realizes braking energy recovery as an additional function. To this end, harmonics brought by diode rectifiers are reduced while rejecting ZSCC. Meanwhile, braking energy can feedback to the city grid with lower harmonics. Finally, simulation and experiment using a 1-kW prototype converter verify the feasibility and validity of the proposed converter on harmonics suppression and braking energy recovery.

KEYWORDS:

1.      Active power filter (APF)

2.       LLC series resonant converter

3.      Soft switching

4.      Braking energy recovery

5.      Zero sequence circulating current (ZSCC)

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Figure 1. Topology of the shunt isolated APF with common DC link integrating braking energy recovery based on HFPET and LLC converter.

 EXPECTED SIMULATION RESULTS:

Figure 2. Load current iL(A), grid current i_g(A) and circulating current i_cc(A). ZSCC of shunt APF directly connected to 3-phase grid without HFPET i_{cc_nonisolated} (A) and ZSCC of shunt isolated APF with HFPET i_{cc_isolated} (A).

Figure 3. Simulation results of current on side of grid i_ga(A), i_gb(A), i_gc (A) and voltage of DC traction grid U_dc (V) under periods of without APF (running process of train), with APF (running process of train), mode switching period and braking energy recovery.

Figure 4. Simulation waves of non-linear load current i_La(A) and

feedback current i_fa (A).

CONCLUSION:

In urban rail transit, harmonics need to be suppressed and braking energy also should be utilized to reduce losses. In this paper, focuses on the problems of harmonics in urban rail transit while braking energy recovery is also included. Based on traditional shunt non-isolated APFs, it is shown that ZCSS   would occur without an isolated HFPET, the amplitude of which is 23% of the load current which brings high losses and increases current stress of the switches. Two types of potential loops of ZCSS are analyzed and equivalent circuits are built for accurate analysis, which shows that the modulation radio of the inverter would be constrained at the upper limit of π/6 to guarantee no ZSCC. Consequently, a shunt isolated  APF with a common DC link integrating braking energy recovery is put forward to realize suppression of harmonics and elimination of ZSCC together with energy feedback. In this topology, the LLC series resonant converter operates in soft-switching condition of ZVS and ZCS, bringing high efficiency and wide voltage range. Closed-loop control strategy of voltage and current during period of APFs and braking energy recovery are designed respectively. During the process of starting and running of the train, the voltage of the DC bus is lower than the reference voltage, the converter  is operating as the APF without ZSCC. In the process of braking, the voltage of the DC bus rises so that APF is paused and braking energy recovery is put into use. Simulation based on MATLAB/Simulink and PLECS has been done to verify analysis on characteristics of soft-switching and eliminating harmonics. A 1-kW prototype based on DSP and CPLD has been built to realize compensation of harmonics and energy feedback. All the needs are well satisfied and this novel converter combine two functions together and restrain ZCSS to realize an high DC voltage utilization with a smaller area  and volume compared to traditional methods of achieving the APF and braking energy recovery.

 REFERENCES:

[1] W. Xu, ``Comparisons and comments on harmonic standards IEC 1000-3-6 and IEEE Std. 519,'' in Proc. 9th Int. Conf. Harmon. Qual. Power, Orlando, FL, USA, Oct. 2000, pp. 260_263.

[2] M. Qasim, P. Kanjiya, and V. Khadkikar, ``Optimal current harmonic extractor based on unified ADALINEs for shunt active power filters,'' IEEE Trans. Power Electron., vol. 29, no. 12, pp. 6383_6393, Dec. 2014.

[3] P. H. Henning, H. D. Fuchs, A. D. L. Roux, and H. D. T. Mouton, ``A 1.5-MW seven-cell series-stacked converter as an active power filter and regeneration converter for a DC traction substation,'' IEEE Trans. Power Electron., vol. 23, no. 5, pp. 2230_2236, Sep. 2008.

[4] A. S. Lock, E. R. C. da Silva, M. E. Elbuluk, and D. A. Fernandes, ``An APF-OCC strategy for common-mode current rejection,'' IEEE Trans. Ind. Appl., vol. 52, no. 6, pp. 4935_4945,  Dec. 2016.

[5] H. Hu, Z. He, and S. Gao, ``Passive filter design for china high-speed rail-way with considering harmonic resonance and characteristic harmonics,'' IEEE Trans. Power Del., vol. 30, no. 1, pp. 505_514, Feb. 2015.

Coordination control of hybrid AC/DC Microgrid

 ABSTRACT:

The hybrid AC/DC microgrid is considered to be the more and more popular in power systems as increasing DC loads. In this study, it is presented that a hybrid AC/DC microgrid is modelled with some renewable energy sources (e.g. solar energy, wind energy), typical storage facilities (e.g. batteries), and AC, DC load, and also the power could be transformed smoothly between the AC and DC sub-grids by the bidirectional AC/DC converter. Meanwhile, coordination control strategies are proposed for power balance under various operations. In grid-connected mode, the U–Q (DC bus voltage and reactive) or PQ method is adopted for the bidirectional AC/DC converter according to the amount of exchange power between AC and DC system in order to improve the DG utilisation efficiency, protecting the converter and maintain the stable operation of the system. In islanded mode, V/F control is applied to stabilising the entire system voltage and frequency, achieving the power balance between the AC and DC systems. Finally, these control strategies are verified by simulation with the results showing that the control scheme would maintain stable operation of the hybrid AC/DC microgrid.

SOFTWARE: MATLAB/SIMULINK

 BLOCK DIAGRAM:

Fig. 1 Compact hybrid AC/DC microgrid system

 EXPECTED SIMULATION RESULTS:

Fig. 2 AC bus voltage and current of A phase in grid-connected mode

Fig. 3 SOC of the battery in grid-connected mode

Fig. 4 Power of wind, DC side power flowed into AC side and the output

of battery in grid-connected mode

Fig. 5 PV output power versus 50*solar irradiation in islanded mode

Fig. 6 DC bus voltage with the influence of solar irradiance variation

and pulse load

Fig. 7 SOC of the battery in islanded mode

Fig. 8 AC bus voltage and current of A phase in islanded mode

Fig. 9  Power of wind, DC side power flowed into AC side and the output

of battery in islanded mode

 CONCLUSION:

In this paper, the coordination control strategies are proposed for the hybrid AC/DC microgrid, operating in grid-connected mode and islanded mode. The control strategies are verified with Matlab/ Simulink under various operations and load conditions. The simulation results show that the control strategies of the hybrid AC/DC microgrid system are efficient. In grid-connected mode, both the bidirectional AC/DC converter and the batteries can keep the DC bus voltage stable, and ensure the converter smoothly operates in U–Q or PQ methods under the various solar irradiation conditions. In islanded mode, the AC bus voltage and frequency are provided by bidirectional AC/DC converter, the battery is to maintain DC bus stability and system power balance under pulse load and various solar irradiation conditions.

REFERENCES:

[1] Unamuno, E., Barrena, J.: ‘Hybrid ac/dc microgrids – part I: review and classification of topologies’, Renew. Sust. Energy Rev., 2015, 52, pp. 1251– 1259

[2] Khederzadeh, M., Sadeghi, M.: ‘Virtual active power filter: a notable feature for hybrid ac/dc microgrids’, IET Gener. Transm. Distrib., 2016, 10, (14), pp. 3539–3546

[3] Salomonsson, D., Soder, L., Sannino, A.: ‘An adaptive control system for a dc microgrid for data centers’, IEEE Trans. Ind. Appl., 2008, 44, (6), pp. 1910– 1917

[4] Anand, S., Fernandes, B.G., Guerrero, J.M.: ‘Distributed control to ensure proportional load sharing and improve voltage regulation in low-voltage dc microgrids’, IEEE Trans. Power Electron., 2013, 28, (4), pp. 1900–1913

[5] Wu, W., Wang, H., Liu, Y., et al.: ‘A dual buck-boost AC/DC converter for DC nanogrid with three terminal outputs’, IEEE Trans. Ind. Electron., 2017, 64, (1), pp. 295–299

A Single-Phase Buck-Boost Matrix Converter with Only Six Switches and Without Commutation Problem

ABSTRACT:

 In this paper, a single-phase buck-boost matrix converter is proposed which can both buck and boost the input voltage with step-changed frequency. It consists of only six unidirectional current flowing bidirectional voltage blocking switches, two input and output filter capacitors, and one inductor. It has following advantages over the existing single-phase matrix converters: 1) it can both buck and boost input voltage solving the limited voltage transfer ratio (only boost or buck) problem; 2) it also has enhanced reliability as it is immune from shoot-through problem of voltage source when all switches are turned-on simultaneously, and therefore, it has no need of PWM dead times and RC snubbers or dedicated soft-commutation strategies to solve the commutation problem; 3) it can also use high speed power MOSFETs as their body diodes never conduct, which eliminate their poor reverse recovery problem. The operation principle of the proposed converter is given, and switching strategies are developed to obtain various multiples and submultiples of input frequency. To verify its performance, a laboratory prototype is fabricated and experiments are performed to produce step-down and step-up voltage with three different frequencies of 120, 60 and 30 Hz.

KEYWORDS:

1.      Buck-boost operation

2.      Commutation problem

3.      Single-phase matrix converter

4.      Step-changed frequency

5.      Z-source

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig. 1. Circuit topology of the proposed single-phase buck-boost MC.

 EXPERIMENTAL RESULTS:

Fig. 2. Experimental results of the proposed ac-ac converter under non-inverting buck-boost mode operations for  and   . (a) Boost operation when,  . (b) Buck operation when ,  . (c) Components stresses. (d) Zoom-in waveforms of (c).

Fig. 3. Experimental results of the proposed ac-ac converter under inverting buck-boost mode operations for   and  . (a) Boost operation when . (b) Buck operation when . (c) Components stresses. (d) Zoom-in waveforms

of (c).

Fig. 4. Experimental results of the proposed ac-ac converter under buck-boost mode operations for  and step-down frequency operation when . (a) Boost operation when . (b) Buck operation when . (c) Switch voltage and inductor current stresses (d) Zoom-in waveforms of (c).

Fig. 5. Experimental results of the proposed ac-ac converter under buck-boost mode operations for  and   step-up frequency operation when . (a) Boost operation when. (b) Buck operation when . (c) Switch voltage and inductor current stresses (d) Zoom-in waveforms of (c).

Fig. 6. Experimental waveforms of input voltage , output voltage , input current 

, and output current during 60 Hz inverting mode operation with inductive load    when 

 Fig. 7. Experimental waveforms of input voltage , output voltage , input current , and output current during 30 Hz mode operation with inductive load when 

Fig. 8. Efficiency of the proposed single-phase buck-boost matrix converter.

CONCLUSION:

In this paper, a single-phase buck-boost MC is proposed which consists of one inductor, two filter capacitors, and six unidirectional current conducting bidirectional voltage blocking switches. It can step-changed the output frequency with both voltage buck and boost operation, therefore, solves the limited gain (only buck or boost) ability of the existing single-phase MCs. The proposed single-phase MC is more reliable than the existing MCs as it can turn on all switches simultaneously without current overshoot problem caused by short-circuit of voltage source. Therefore, it does not have commutation problem and eliminates the need for PWM dead times and lossy RC snubbers or dedicated soft-commutation strategies, which is a significant advantage.

A detailed analysis of the proposed topology and switching strategies are given for buck-boost operation with step-down, same and step-up frequency. A scaled down laboratory prototype of the proposed MC with output voltage of 70 Vrms was fabricated based on TMS320F28335 DPS-kit to generate the control signals, and experimental results under buck and boost modes were given for output frequencies of 30 Hz (step-down frequency), 60 Hz (same frequency) and 120 Hz (step-up frequency). The proposed MC can be used in applications which require voltage regulation along with frequency variation such as to control the speed of a fan or a pump, to drive induction motor, for induction heating, and to implement a high boost AC-DC MC based on Cockcroft-Walton voltage multiplier, etc.

REFERENCES:

[1] B. H. Kwon, B. D. Min, and J. H. Kim, “Novel topologies of AC choppers,” IEE Proc. Electr. Power Appl., vol. 143, no. 4, pp. 323–330, Jul. 1996.

[2] X. P. Fang, Z. M. Qian, and F. Z. Peng, “Single-phase Z-source PWM ac–ac converters,” IEEE Power Electron. Lett., vol. 3, no. 4, pp. 121–124, Dec. 2005.

[3] T. B. Lazzarin, R. L. Andersen, and I. Barbi, “A switched-capacitor three-phase ac-ac converter,” IEEE Trans. Ind. Electron., vol. 62, no. 2, pp. 735–745, Feb. 2015.

[4] D.-C. Lee, and Y.-S. Kim, “Control of single-phase-to-three-phase ac/dc/ac PWM converters for induction motor drives,” IEEE Trans. Ind. Electron., vol. 54, no. 2, pp. 797– 804, Apr. 2007.

[5] J. E. C. d. Santos, C. B. Jacobina, N. Rocha, and E. R. C. d. Silve, “Six-phase machine drive system with reversible parallel ac-dc-ac converters,” IEEE Trans. Ind. Electron., vol. 58, no. 5, pp. 2049– 2053, May. 2011.