Power Quality Assessment of Voltage Positive Feedback Based Islanding Detection Algori

 ABSTRACT:

 

Islanding refers to a condition where distributed generators (DGs) inject power solely to the local load after electrical separation from power grid. Several islanding detection methods (IDMs) categorized into remote, active, and passive groups have been reported to detect this undesirable state. In active techniques, a disturbance is injected into the DG’s controller to drift a local yardstick out of the permissible range. Although this disturbance leads to more effective detections even in well-balanced island, it raises the total harmonic distortion (THD) of the output current under the normal operation conditions. This paper analyzes the power quality aspect of the modified sliding mode controller as a new active IDM for grid-connected photovoltaic system (GCPVS) with a string inverter. Its performance is compared with the voltage positive feedback (VPF) method, a well-known active IDM. This evaluation is carried out for a 1 kWp GCPVS in MATLAB/Simulink platform by measuring the output current harmonics and THD as well as the efficiency under various penetration and disturbance levels. The output results demonstrate that since the proposed disturbance changes the amplitude of the output current, it does not generate harmonics/subharmonics. Thereby, it has a negligible adverse effect on power quality. It is finally concluded that the performance of the sliding mode-based IDM is reliable from the standpoints of islanding detection and power quality.

KEYWORDS:

1.      Islanding detection method (IDM)

2.      Power quality

3.      Sliding mode controller

4.       Total harmonic distortion (THD)

5.      Voltage positive feedback (VPF)

 SOFTWARE: MATLAB/SIMULINK

 CIRCUIT DIAGRAM:

 

Fig. 1. Schematic of case study system under evaluation.

 EXPECTED SIMULATION RESULTS:

 

 

Fig. 2. Effect of VPF and proposed schemes on THDI with different percentages

of nominal power.

 

 Fig. 3. Effect of classic VPF and proposed IDM on power quality (harmonic spectra).

 

Fig. 4. Average THDI for different disturbance sizes. (a) Modified sliding

mode. (b) Classic VPF.

 CONCLUSION:

In this paper, the influence of the classic VPF and modified sliding-mode IDM on the GCPVS’s power quality and efficiency has been evaluated. The study has been done for a 1 kWp PV system with string inverter. The simulation results show that, while the THD of output current in the proposed IDM is smaller than the simple VPF, both methods render acceptable power quality in a wide range of system operation. This proper performance has been achieved due to the variation of the current magnitude rather than the angle or frequency. This magnitude variation is realized in VPF and the proposed method in the current and voltage control loops (MPPT), respectively. The simulations also confirm that the acceptable THDI and harmonics are guaranteed in multi-GCPVSs connection situation even at low power generation levels as the worst scenario. Since the new technique tries to deviate the system from its MPP condition, the effect of embedded disturbance on the efficiency is also performed. In this regard, the simulations are carried out and a negligible reduction in MPPT and inverter efficiencies (less than 0.04%) has been demonstrated in the proposed method. This occurs since MPP can be gained at a small bound around ref. It has been finally concluded that the modified slidingmode controller has the advantages of the conventional VPF scheme in islanding detection as well as a higher power quality in the production of energy.

REFERENCES:

[1] A. Jäger-Waldau, “PV status report 2017,” Publications Office of the European Union, Luxembourg, 2018.

[2] M. Sandhu and T. Thakur, “Harmonic minimization in a modified cascaded multilevel inverter for islanded microgrid using two switching techniques,” International Journal of Grid and Distributed Computing, vol. 10, no. 12, pp. 11-20, Dec. 2017.

[3] S. Natarajan and R. S. R. Babu, “Reduction of total harmonic distortion in cascaded H-bridge inverter by pattern search technique,” International Journal of Electrical and Computer Engineering (IJECE), vol. 7, no. 6, p. 3292, Dec. 2017.

[4] A. Luo, Q. Xu, F. Ma et al., “Overview of power quality analysis and control technology for the smart grid,” Journal of Modern Power Systems and Clean Energy, vol. 4, no. 1, pp. 1-9, Jan. 2016.

[5] A. Khamis, H. Shareef, E. Bizkevelci et al., “A review of islanding detection techniques for renewable distributed generation systems,” Renewable and Sustainable Energy Reviews, vol. 28, pp. 483-493, Dec. 2013.

Hybrid converter topology for reducing torque ripple of BLDC motor

 ABSTRACT:

 This study investigates the torque ripple performance of brushless DC (BLDC) motor drive system by integrating both modified single-ended primary inductor converter (SEPIC) and silicon carbide metal–oxide–semiconductor field-effect transistor based three-level neutral-point-clamped (NPC) inverter. In BLDC motor, the high commutation torque ripple is an important origin of vibration, speed ripple and prevents the use of the BLDC motor drive system in high-performance and high-precision applications. For torque ripple reduction, the modified SEPIC converter is employed at the entrance of the three-level NPC inverter, which regulates the DC-link voltage according to the motor speed. Moreover, the three-level NPC inverter is employed as a second-stage converter to suppress current ripple for further torque ripple reduction. Finally, the performance of the proposed hybrid converter topology is verified by simulation and laboratory experimental results.

KEYWORDS:

1.      DSP controller

2.      Energy eficiency

3.      Fuzzy logic (FL)

4.      MPPT

5.      Photovoltaic systems

 SOFTWARE: MATLAB/SIMULINK

 CIRCUIT DIAGRAM:

 

                         Fig. 1 BLDC motor drive system with modified SEPIC converter and three-level NPC inverter

(a) Proposed converter topology

 BLOCK DIAGRAM:

                                                             Fig. 2 BLDC motor drive control strategy

(a) Block diagram of PWM controller for three-level NPC inverter

 

EXPECTED SIMULATION RESULTS:

Fig. 3 Continued

Fig. 4 Phase current and torque waveforms

(a) Phase current and torque waveforms from simulation at 2500 rpm and 0.825 N m, (b) Phase current and torque waveforms from simulation at 2500 rpm and 0.825 N m, (c) Phase current and torque waveforms from simulation at 6000 rpm and 0.825 N m, (d) Phase current and torque waveforms from simulation at 6000 rpm and 0.825 N m

CONCLUSION:

A novel hybrid circuit topology has been proposed in this paper which is built by a modified SEPIC converter and a SiC-MOSFETbased three-level NPC converter for minimising torque ripple in a BLDC motor drive system. For efficient reduction of torque ripple, the first stage is the modified SEPIC converter that lifts the DClink voltage to the desired value based on the motor speed measurement. For further torque ripple reduction, the three-level NPC inverter is employed as the second-stage converter to suppress current ripple. Experimental results show that the proposed hybrid converter topology can suppress the torque ripple to 14.6% at the speed of 6000 rpm, commutation torque ripple is reduced substantially and produce smooth torque waveform than the BLDC motor driven by the two-level, three-level NPC, twolevel inverter with DC-link voltage control, and two-level inverter with SEPIC converter and switch selection circuit topologies.

REFERENCES:

[1] Singh, B., Bist, V.: ‘An improved power quality bridgeless Cuk converter fed BLDC motor drive for air conditioning system’, IET Power Electron., 2013, 6, (5), pp. 902–913

[2] Carlson, R., Lajoie-Mazenc, M., Fagundes, J.C.D.S.: ‘Analysis of torque ripple due to phase commutation in brushless dc machines’, IEEE Trans. Ind. Appl., 1992, 28, (3), pp. 632–638

[3] Lee, S.K., Kang, G.H., Hur, J., et al.: ‘Stator and rotor shape designs of interior permanent magnet type brushless DC motor for reducing torque fluctuation’, IEEE Trans. Magn., 2012, 48, pp. 4662–4665

[4] Seo, U.J., Chun, Y.D., Choi, J.H., et al.: ‘A technique of torque ripple reduction in interior permanent magnet synchronous motor’, IEEE Trans. Magn., 2011, 47, (10), pp. 3240–3243

[5] Murai, Y., Kawase, K., Ohashi, K., et al.: ‘Torque ripple improvement for brushless DC miniature motors’, IEEE Trans. Ind. Appl., 1989, 25, (3), pp. 441–450

Voltage Sag Enhancement of Grid Connected Hybrid PV-Wind Power System Using Battery and SMES Based Dynamic Voltage Restorer

 ABSTRACT:

 Renewable energy sources; which are abundant in nature and climate friendly are the only preferable choice of the world to provide green energy. The limitation of most renewable energy sources specifically wind and solar PV is its intermittent nature which are depend on wind speed and solar irradiance respectively and this leads to power fluctuations. To compensate and protect sensitive loads from being affected by the power distribution side fluctuations and faults, dynamic voltage restorer (DVR) is commonly used. This research work attempts to withstand and secure the effect of voltage fluctuation of grid connected hybrid PV-wind power system. To do so battery and super magnetic energy storage (SMES) based DVR is used as a compensating device in case of voltage sag condition. The compensation method used is a pre-sag compensation which locks the instantaneous real time three phase voltage magnitude and angle in normal condition at the point of common coupling (PCC) and stores independently so that during a disturbance it used for compensation. Symmetrical and asymmetrical voltage sags scenario are considered and compensation is carried out using Power System Computer Aided Design or Electro Magnetic Transient Design and Control (PSCAD/EMTDC) software.

KEYWORDS:

1.      Dynamic voltage restorer (DVR)

2.      energy storage

3.      intermittent

4.      power quality

5.      voltage sag compensation

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

 

FIGURE 1. On grid PV-wind hybrid system

EXPECTED SIMULATION RESULTS:

 

                                                                                   (a)

(b)

(c)

FIGURE 2. Simulation results and DVR response for 25% symmetrical voltage sag case (a) load voltage without DVR, (b) DVR injected voltage and (c) load voltage with DVR

 

(a)

(b)

(c)

FIGURE 3. Simulation results and DVR response for 12% symmetrical voltage sag case (a) load voltage without DVR, (b) DVR injected voltage and (c) load voltage with DVR

(a)

(b)

(c)

FIGURE 4. Simulation results and DVR response for 25% asymmetrical voltage sag case (a) load voltage without DVR, (b) DVR injected voltage and (c) load voltage with DVR

(a)

(b)

(c)

FIGURE 5. Simulation results and DVR response for 35% asymmetrical voltage sag case (a) load voltage without DVR, (b) DVR injected voltage and (c) load voltage with DVR

 

CONCLUSION:

In this paper, a voltage sag enhancement of sensitive load which gets power from grid connected PV-wind power system is demonstrated using HES based DVR. The proposed DVR targets to protect the sensitive load from affected by any voltage fluctuation which arise either from fault condition or unstable power output of PV-wind system. The control and operations of BES and SMES devices is developed by observing voltage condition of the grid at the PCC and the SOC levels of battery and SMES. In addition to this, for full realization of the proposed DVR system the control and operation of the VSC is developed by observing the voltage level at the PCC. The pre-sag compensation strategy is selected based on the capability of both magnitude and phase jump restoration. Based on the conditions, three operating states of the HES based DVR are defined, which are normal (idle state), charging state and discharging state. The effectiveness of the proposed operating states has been demonstrated in realistic cases. In the simulation, different voltage sag depth scenarios are considered for both symmetrical and asymmetrical voltage imbalances and the HES based DVR works well. A combination of voltage sag, voltage swell and harmonics scenarios will be demonstrated in the future works.

REFERENCES:

[1] BP Statistical Review of World Energy, 68th ed. 2019.

[2] M. R. Banaei and S. H. Hosseini, “Verification of a new energy control strategy for dynamic voltage restorer by simulation,” vol. 14, pp. 112–125, 2006.

[3] IRENA, Future of wind: Deployment, investment, technology, grid integration and socio-economic aspects (A Global Energy Transformation paper). International Renewable Energy Agency, Abu Dhabi, 2019.

[4] IRENA, Future of Solar Photovoltaic: Deployment, investment, technology, grid integration and socio-economic aspects (A Global Energy Transformation: paper). International Renewable Energy Agency, Abu Dhabi, 2019.

[5] H. M. Al-masri, S. Member, M. Ehsani, and L. Fellow, “Feasibility Investigation of a Hybrid On-Grid Wind Photovoltaic Retrofitting System,” IEEE Trans. Ind. Appl., vol. 52, no. 3, pp. 1979–1988, 2016.

Power Quality Improvement and Low Voltage Ride through Capability in Hybrid Wind-PV Farms Grid-Connected Using Dynamic Voltage Restorer

ABSTRACT:

 

The paper proposes the application of a Dynamic Voltage Restorer (DVR) to enhance the power quality and improve the low voltage ride through (LVRT) capability of a three-phase medium-voltage network connected to a hybrid distribution generation (DG) system. In this system, the photovoltaic (PV) plant and the wind turbine generator (WTG) are connected to the same point of common coupling (PCC) with a sensitive load. The WTG consists of a DFIG generator connected to the network via a step-up transformer. The PV system is connected to the PCC via a two-stage energy conversion (DC-DC converter and DC-AC inverter). This topology allows, first, the extraction of maximum power based on the incremental inductance technique. Second, it allows the connection of the PV system to the public grid through a step-up transformer. In addition, the DVR based on Fuzzy Logic Controller (FLC) is connected to the same PCC. Different fault condition scenarios are tested for improving the efficiency and the quality of the power supply and compliance with the requirements of the LVRT grid code. The results of the LVRT capability, voltage stability, active power, reactive power, injected current, and DC link voltage, speed of turbine and power factor at the PCC are presented with and without the contribution of the DVR system.

KEYWORDS:

1.      Active power

2.      DC-link voltage DFIG

3.      Dynamic Voltage Restorer

4.      LVRT

5.      Power Factor

6.      Photovoltaic

7.      Voltage Stability

8.      Reactive Power

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

 

FIGURE 1: PV-WTG hybrid system with DVR and a load connected to grid.

 

EXPECTED SIMULATION RESULTS:

 

FIGURE 2: Voltage phase magnitude at PCC during faults with typical LVRT and HVRT characteristics requirements of Distributed Generation Code of Germany as an example.

FIGURE 3: Voltage phase magnitude at PCC during sag fault.

 

FIGURE 4: Voltage phase magnitude at PCC during short circuit fault.

 

 FIGURE 5: Phase voltage at PCC during sag fault.

 

FIGURE 6: DVR voltage contribution at PCC during sag fault.

FIGURE 7: Phase voltage at PCC during short circuit fault.

  

FIGURE 8: Total active power of hybrid system at PCC injected to grid.

 

 

FIGURE 9: PV active power at PCC injected to grid.

 

FIGURE 10: Wind active power at PCC injected to grid.

 

FIGURE 11: Total reactive power of hybrid system at PCC injected to grid.

 

FIGURE 12: PV reactive power at PCC injected to grid.

 

 FIGURE 13: Wind reactive power at PCC injected to grid.

 FIGURE 14: Total PV-WT current injected to grid at PCC.

FIGURE 15: PV current injected at PCC.

FIGURE 16: WT current injected at PCC to grid.

 

FIGURE 17: Power factor at PCC.

 

FIGURE 18: Turbine rotor speed.

 

FIGURE 19: Vdc link at WTG inverter.

 

 FIGURE 20: Vdc link voltage at PV inverter.

 

CONCLUSION:

The simulation study was carried out using MATLAB to demonstrate the effectiveness of the proposed DVR control system to improve the power quality and LVRT capability of the hybrid PV-WT power system. The system has been tested under different fault condition scenarios. The results have shown that the DVR connected to the PV-Wind hybrid system at the medium voltage grid is very effective and is able to mitigate voltage outages and short circuit failure with improved voltage regulation capabilities and flexibility in the correction of the power factor.

The results of the simulation also prove that the system designed is secure since the required voltage ranges are respected correctly and the DG generators operate reliably. The main advantage of the proposed design is the rapid recovery of voltage; the power oscillations overshoot reduction, control of rotor speed and preventing the system from having a DC link overvoltage and thus increasing the stability of the power system in accordance with LVRT requirements.

REFERENCES:

[1] J. Hossain, H. Roy Pota, “Robust Control for Grid Voltage Stability High Penetration of Renewable Energy,” Springer ,1st ed., pp.1–11, 2014.

[2] S. Talari et al.,"Stochastic modelling of renewable energy sources from operators' point-of-view: A survey," Renewable and Sustainable Energy Reviews, Vol.81, no.2, , pp.1953-1965,Jan.2018.

[3] R. Teodorescu ,M. Liserre, P. Rodríguez, “Grid Converters For Photovoltaic And Wind Power Systems, “John Wiley & Sons Ltd.,1st ed.,2011.

[4] G. Romero Rey, L. M.Muneta, “Electrical Generation and Distribution Systems and Power Quality Disturbances,” InTech, 1st ed., 2011.

[5] L.Ruiqi, G.Hua, Y.Geng, “Fault ride-through of renewable energy conversion systems during voltage recovery,” J. Mod. Power Syst. Clean Energy,vol. 4,no.1,pp:28-39, 2016.