Hybrid Active Filter with Variable Conductance for Harmonic Resonance Suppression in Industrial Power Systems

ABSTRACT:

Unintentional series and/or parallel resonances, due to the tuned passive filter and the line inductance, may result in severe harmonic distortion in the industrial power system. This paper presents a hybrid active filter to suppress harmonic resonance and to reduce harmonic distortion. The proposed hybrid filter is operated as variable harmonic conductance according to the voltage total harmonic distortion; therefore, harmonic distortion can be reduced to an acceptable level in response to load change or parameter variation of the power system. Since the hybrid filter is composed of a seventh-tuned passive filter and an active filter in series connection, both dc voltage and kVA rating of the active filter are dramatically decreased compared with the pure shunt active filter. In real application, this feature is very attractive since the active power filter with fully power electronics is very expensive. A reasonable tradeoff between filtering performances and cost is to use the hybrid active filter. Design consideration are presented, and experimental results are provided to validate effectiveness of the proposed method. Furthermore, this paper discusses filtering performances on line impedance, line resistance, voltage unbalance, and capacitive filters.

KEYWORDS:

1.      Harmonic resonance

2.       Hybrid active filter

3.      Industrial power system

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. Proposed HAFU in the industrial power system and its associated control. (a) Circuit diagram of the HAFU. (b) Control block diagram of the HAFU.

EXPECTED SIMULATION RESULTS:

             

Fig. 2. Line voltage e, source current i_s, load current i_L, and filter current i in the case of NL₁ initiated. X-axis: 5 ms/div. (a) HAFU is off. (b) HAFU is on.

Fig. 3. Line voltage e, source current i_s, load current i_L, and filter current i in the case of NL₂ initiated. X-axis: 5 ms/div. (a) HAFU is off. (b) HAFU is on.

Fig. 4. Transient response when the nonlinear load is increased at T. (a)Waveforms of v_dc, Voltage THD, G^*. X-axis: 100 ms/div; Y -axis: v_dc (V), G^* (1.21 p.u./div), and THD (1.25%/div). (b) Current waveforms.

Fig. 5. HAFU is off for single-phase nonlinear load. (a) Terminal voltage. (b) Source current. (c) Filter current. (d) Load current.

Fig. 6. HAFU is on for single-phase nonlinear load. (a) Terminal voltage. (b) Source current. (c) Filter current. (d) Load current.

CONCLUSION:

This paper presents a hybrid active filter to suppress harmonic resonances in industrial power systems. The proposed hybrid filter is composed of a seventh harmonic-tuned passive filter and an active filter in series connection at the secondary side of the distribution transformer. With the active filter part operating as variable harmonic conductance, the filtering performances of the passive filter can be significantly improved. Accordingly, the harmonic resonances can be avoided, and the harmonic distortion can be maintained inside an acceptable level in case of load changes and variations of line impedance of the power system. Experimental results verify the effectiveness of the proposed method. Extended discussions are summarized as follows.

• Large line inductance and large nonlinear load may result in severe voltage distortion. The conductance is increased to maintain distortion to an acceptable level.

• Line resistance may help reduce voltage distortion. The conductance is decreased accordingly.

• For low line impedance, THD^* should be reduced to enhance filtering performances. In this situation, measuring voltage distortion becomes a challenging issue.

• High-frequency resonances resulting from capacitive filters is possible to be suppressed by the proposed method.

• In case of unbalanced voltage, a band-rejected filter is needed to filter out second-order harmonics if the SRF is realized to extract voltage harmonics.

 REFERENCES:

 [1] R. H. Simpson, “Misapplication of power capacitors in distribution systems with nonlinear loads-three case histories,” IEEE Trans. Ind. Appl., vol. 41, no. 1, pp. 134–143, Jan./Feb. 2005.

[2] T. Dionise and V. Lorch, “Voltage distortion on an electrical distribution system,” IEEE Ind. Appl. Mag., vol. 16, no. 2, pp. 48–55, Mar./Apr. 2010.

[3] E. J. Currence, J. E. Plizga, and H. N. Nelson, “Harmonic resonance at a medium-sized industrial plant,” IEEE Trans. Ind. Appl., vol. 31, no. 4, pp. 682–690, Jul/Aug. 1995.

[4] C.-J. Wu et al., “Investigation and mitigation of harmonic amplification problems caused by single-tuned filters,” IEEE Trans. Power Del., vol. 13, no. 3, pp. 800–806, Jul. 1998.

[5] B. Singh, K. Al-Haddad, and A. Chandra, “A review of active filters for power quality improvement,” IEEE Trans. Ind. Electron., vol. 46, no. 5, pp. 960–971, Oct. 1999.

A Transformerless Grid Connected Photovoltaic Inverter with Switched Capacitors

ABSTRACT:

In the transformerless photovoltaic (PV) system, the common mode ground leakage current may appear due to the galvanic connection between the PV array and the ground, which causes the safety issues and reduces the efficiency. To solve this problem, a novel inverter topology with switched capacitors is proposed in this paper. By connecting one pole of the PV cell directly to the neutral line of the grid, the common mode current is eliminated. Meanwhile, the switched capacitor technology is applied to increase the DC voltage utilization rate. Furthermore, a modified unipolar sinusoidal pulse width modulation (SPWM) strategy is proposed to reduce the pulsating current caused by the charging and discharging operations of the switched capacitors. Also, several optimization principles are put forward to further reduce the pulsating current to improve the efficiency and reliability. Finally, the proposed topology and modulation strategy are verified with simulation and a 250W experimental prototype.

SOFTWARE: MATLAB/SIMULINK

 CIRCUIT DIAGRAM:

Fig 1. Proposed topology.

EXPECTED SIMULATION RESULTS:

                                            Fig 2. Simulated Waveforms Of Output Current And Current Stress On S3

With Different Ratio Of C1/(C1+C2).

 Fig 3. Experimental Waveforms Of Igrid And Vgrid.

Fig 4. Current And Voltage Stress On S3.

(a)     C1/(C1+C2)=0.33 (C1 = 470μf, C2 = 940μf), Vbus = 400V

                                         (b)     C1/(C1+C2) =0.67 (C1 = 940μf, C2 = 470μf), Vbus = 400V

        

(C) C1/(C1+C2) =0.33 (C1 = 470μf, C2 = 940μf), Vbus = 380V

Fig 5. Current Stress On S3 Under Different Conditions.

CONCLUSION:

A novel transformerless inverter topology with the switched capacitors is proposed for the grid connected PV power generation system. Only five power switches are required in the proposed PV inverter topology. The common mode current is eliminated perfectly. The DC input voltage required is the same as the full bridge inverter. A modified unipolar SPWM strategy is proposed for the topology, enabling it to output three voltage levels. It is also guaranteed that C2 is charged every switching cycle under this SPWM strategy, so that the current pulse on the power devices caused by the switched capacitors is reduced. Furthermore, based on the quantitative analysis of the devices’ current stress, the principles for optimizing the capacitances of the switched capacitors C1 and C2 are given. The simulation and experimental results are provided to verify the theoretical analysis.

REFERENCES:

[1] Gonzalez R, Gubia E, Lopez J, Marroyo L, “Transformerless Single- Phase Multilevel-Based Photovoltaic Inverter,” IEEE Transactions on HIndustrial Electronics, Hvol. 55, Hno. 7, Hpp. 2694-2702, 2008.

[2] Lopez O, Freijedo F.D, Yepes A.G, Fernandez-Comesaa P, Malvar J, Teodorescu R, Doval-Gandoy J, “Eliminating Ground Current in a Transformerless Photovoltaic Application,” IEEE Transactions on Energy conversion, vol. 25, no. 1, pp. 140-147, 2010.

[3] Araujo S.V, Zacharias P, Sahan B, “Novel Grid-Connected Non- Isolated Converters for Photovoltaic Systems with Grounded Generator,” in HPower Electronics Specialists Conference, H2008, pp. 58-65.

[4] Lopez O, Teodorescu R, Doval-Gandoy J, “HMultilevel transformerless topologies for single-phase grid-connected converters,” in IEEE Industrial Electronics, IECON 2006-32nd Annual Conference on Digital Object Identifier, 2006, pp. 5191-5196.

Single-Phase Seven-Level Grid-Connected Inverter for Photovoltaic System

ABSTRACT:

This paper proposes a single-phase seven-level inverter for grid-connected photovoltaic systems, with a novel pulse width-modulated (PWM) control scheme. Three reference signals that are identical to each other with an offset that is equivalent to the amplitude of the triangular carrier signal were used to generate the PWM signals. The inverter is capable of producing seven levels of output-voltage levels (V_dc, 2V_dc/3, V_dc/3, 0,−V_dc,−2V_dc/3,−V_dc/3) from the dc supply voltage. A digital proportional–integral current-control algorithm was implemented in a TMS320F2812 DSP to keep the current injected into the grid sinusoidal. The proposed system was verified through simulation and implemented in a prototype.

KEYWORDS:

1.      Grid connected

2.      Modulation index

3.       Multilevel inverter

4.       Photovoltaic (PV) system

5.       Pulse width-modulated (PWM)

6.      Total harmonic distortion (THD)

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig. 1. Proposed single-phase seven-level grid-connected inverter for photovoltaic

systems.

EXPECTED SIMULATION RESULTS:

            Fig. 2. PWM signals for S₁ and S₃.

        

Fig. 3. PWM signals for S₂ and S₄.

Fig. 4. PWM signals for S₅ and S₆.

Fig. 5. Inverter output voltage (V_inv).

Fig. 6. Grid voltage (V_grid) and grid current (I_grid).

CONCLUSION:

Multilevel inverters offer improved output waveforms and lower THD. This paper has presented a novel PWM switching scheme for the proposed multilevel inverter. It utilizes three reference signals and a triangular carrier signal to generate PWM switching signals. The behavior of the proposed multilevel inverter was analyzed in detail. By controlling the modulation index, the desired number of levels of the inverter’s output voltage can be achieved. A TMS320F2812 DSP optimized the performance of the inverter. The less THD in the seven-level inverter compared with that in the five- and three-level inverters is an attractive solution for grid-connected PV inverters.

REFERENCES:

[1] M. Calais and V. G. Agelidis, “Multilevel converters for single-phase grid connected photovoltaic systems—An overview,” in Proc. IEEE Int. Symp. Ind. Electron., 1998, vol. 1, pp. 224–229.

[2] S. B. Kjaer, J. K. Pedersen, and F. Blaabjerg, “A review of single-phase grid connected inverters for photovoltaic modules,” IEEE Trans. Ind. Appl., vol. 41, no. 5, pp. 1292–1306, Sep./Oct. 2005.

[3] P. K. Hinga, T. Ohnishi, and T. Suzuki, “A new PWM inverter for photovoltaic power generation system,” in Conf. Rec. IEEE Power Electron. Spec. Conf., 1994, pp. 391–395.

[4] Y. Cheng, C. Qian, M. L. Crow, S. Pekarek, and S. Atcitty, “A comparison of diode-clamped and cascaded multilevel converters for a STATCOM with energy storage,” IEEE Trans. Ind. Electron., vol. 53, no. 5, pp. 1512– 1521, Oct. 2006.

[5] M. Saeedifard, R. Iravani, and J. Pou, “A space vector modulation strategy for a back-to-back five-level HVDC converter system,” IEEE Trans. Ind. Electron., vol. 56, no. 2, pp. 452–466, Feb. 2009.

Stability Enhancement of Wind Power System by using Energy Capacitor System

ABSTRACT:

This paper presents Permanent Magnet Synchronous generator (PMSG) based a variable speed wind turbine systems including energy capacitor system (ECS). The ECS is the combination of electric double layer capacitor (EDLC) known as super capacitor and power electronic devices for wind power application with its detailed modeling and control strategy which can supply smooth electrical power to the power grid and makes the system better stable and reliable. As generated power from wind fluctuates randomly, the objective of this control system is to select a line power reference level and to follow the reference level by absorbing or providing active power to or from ECS to smooth output power fluctuation penetrated to the grid and to keep the wind farm terminal voltage at a desired level by supplying necessary reactive power. The performance of the proposed system is investigated by simulation analysis using PSCAD/EMTDC software.

KEYWORDS:

1.      Variable speed wind generator

2.       Permanent Magnet Synchronous generator (PMSG)

3.       Energy Capacitor System (ECS)

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. Model System

 EXPECTED SIMULATION RESULTS:

Fig. 2. Response of real wind speed data [case-I]

Fig. 3. Response of PMSG generated Active Power [case-I]

 

Fig. 4. Grid terminal voltage without & with ECS [case-I]

Fig. 5. Grid Power with/without EDLC and EDLC power [case-I]

Fig. 6. Grid Active Power without and with EDLC [case-I]

Fig. 7. EDLC active Power [case-I]

Fig. 8. EDLC energy [case-I]

Fig. 9. Comparison with SMA and ECS

Fig. 10. Response of Wind speed [case-II]

Fig. 11. PMSG generated Active Power [MW] [case-II]

Fig. 12. Grid Active Power without and with EDLC [case-II]

Fig. 13. EDLC active power [case-II]

Fig. 14. EDLC energy [case-II]

Fig. 15. Grid terminal voltage without & with ECS [case-II].

Fig. 16. Frequency deviation of SMA, ECS & without ECS [case-I].

             

CONCLUSION:

The simulation results show that the quality of the terminal voltage and output power penetrated to the grid is not good but continuously varying without ECS system. Besides, when we used ECS system, the terminal voltage and grid power is almost constant and quality of voltage and power is excellent. So, using ECS system smoothed power can be supplied to the grid by charging and discharging of EDLC. By using low pass filter to calculate line power reference instead of SMA, EMA makes the system very simple, compact and cost effective. Therefore, it can be concluded that this proposed system can be applied effectively in power systems to generate high quality electrical power from the natural fluctuating wind.

REFERENCES:

[1] G. annual report, 2014; world wind energy association.

[2] Niu Jiangang, Baotou, “Investigation on the properties of fly ash concrete attacked by a Pseudo-capacitance Faradaic electrochemical storage with electron charge-transfer, achieved by redox reactions, intercalation or electrosorption. Rain,” IEEE, Conference, ICETCE, Lushan, DOI. 10, pp. 2335 – 2339, 22-24 April 2011.

[3] Harden F, Bleijis JAM, Jones R, Bromely P, Ruddell AJ, “Application of power-controlled flywheel drive for wind power conditioning in a wind /diesel power system,” Ninth international conference on Electrical Machines and Drives, Canterbury, paper no. 468, pp. 65-70.

[4] Senjyu T., Sakamoto R., Urasaki N., Funabashi T. Fujita H., SekineH.,“Output power leveling of wind turbine Generator for all operating regions by pitch angle control,” Energy Conversion, IEEE Transactions, Vol. 21, pp. 467 - 475, 2006.

[5] Ali MH, Murata T, Tamura J, “Minimization of fluctuations of line power and terminal voltage of wind generator by fuzzy logiccontrolled SMES,” international review of Electrical engineering, vol. 1, pp. 559-566, 2006.