Power Quality Enhancement in Residential Smart Grids through Power Factor Correction Sta

ABSTRACT:

The proliferation of non-linear loads and the increasing penetration of Distributed Energy Resources (DER) in Medium-Voltage (MV) and Low-Voltage (LV) distribution grids, make it more difficult to maintain the power quality levels in residential electrical grids, especially in the case of weak grids. Most household appliances contain a conventional Power Factor Corrector (PFC) rectifier, which maximizes the load Power Factor (PF) but does not contribute to the regulation of the voltage Total Harmonic Distortion (THDV ) in residential electrical grids. This manuscript proposes a modification for PFC controllers by adapting the operation mode depending on the measured THDV . As a result, the PFCs operate either in a low current Total Harmonic Distortion (THDI ) mode or in the conventional resistor emulator mode and contribute to the regulation of the THDV and the PF at the distribution feeders. To prove the concept, the modification is applied to a current sensorless Non-Linear Controller (NLC) applied to a single-phase Boost rectifier. Experimental results show its performance in a PFC front-end stage operating in Continuous Conduction Mode (CCM) connected to the grid with different THDV .

KEYWORDS:

1.      Harmonic distortion

2.      Non-linear carrier control

3.      Power factor correction

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. Residential LV grid with household appliances feed through conventional AC/DC stages (without the proposed operation mode selector) and the proposed PQE controller.

EXPECTED SIMULATION RESULTS:

Fig. 2. Experimental results of PQE PFC at 50 Hz. Voltage and current waveforms in a) resistor emulator mode (k = 0), b) sinusoidal current mode (k = 1) and c) measured spectra in both operation modes.

Fig. 3. Experimental results of PQE PFC at 60 Hz. Voltage and current waveforms in a) resistor emulator mode (k = 0), b) sinusoidal current mode (k = 1) and c) measured spectra in both operation modes.

Fig. 4. Experimental results of PQE PFC at 400 Hz. Voltage and current waveforms in a) resistor emulator mode (k = 0), b) sinusoidal current mode (k = 1) and c) measured spectra in both operation modes.

CONCLUSION:

The consequence on the electrical power quality of connecting household appliances to the grid through PFC stages has been assessed considering different THDV scenarios. As has been shown in (17) and (23), there are conditions under which sinusoidal current consumption results in better PF at the PCC than with resistor emulator behavior, commonly assumed to be ideal for PFC stages. A modification of the carrier signal of NLC controllers applied to PFC stages is designed to impress sinusoidal input current despite the input voltage distortion. The line current estimation with no interaction with the power stage implements the NLC with high noise immunity. The digital implementation of the non-linear controller is appropriate to define the carrier and to include additional reduction of the current distortion depending on the application. The PQE controller can be applied to mitigate the effect of nonlinear loads within household appliances on residential electrical grids. The operation mode of the digital controller can be autonomously adjusted through the locally measured THDV , without extra circuitry. The user or a THDV threshold detection selects the convenient behavior (either resistor emulator or pure sinusoidal current). Experimental results obtained with high THDV (above 5 %) confirm the feasibility of the PQE controller in both sinusoidal current and resistive emulator modes.

REFERENCES:

[1] IEEE Std. 519-2014 (Revision of IEEE Std. 519-1992), IEEE Recommended Practice and Requirements for Harmonic Control in ElectricPower Systems, DOI 10.1109/IEEESTD.2014.6826459, pp. 1–29, Jun. 2014.

[2] Y. J. Wang, R. M. O’Connell, and G. Brownfield, “Modeling and prediction of distribution system voltage distortion caused by nonlinear residential loads,” IEEE Trans. Power Del., vol. 16, DOI 10.1109/61.956765, no. 4, pp. 744–751, Oct. 2001.

[3] H. Oraee, “A quantitative approach to estimate the life expectancy of motor insulation systems,” IEEE Trans. Dielectr. Electr. Insul., vol. 7, DOI 10.1109/94.891990, no. 6, pp. 790–796, Dec. 2000.

[4] D. Fabiani and G. C. Montanari, “The effect of voltage distortion on ageing acceleration of insulation systems under partial discharge activity,” IEEE Electr. Insul. Mag., vol. 17, DOI 10.1109/57.925300, no. 3, pp. 24–33, May. 2001.

[5] T. J. Dionise and V. Lorch, “Harmonic filter analysis and redesign for a modern steel facility with two melt furnaces using dedicated capacitor banks,” in IEEE IAS Annual Meeting, vol. 1, DOI 10.1109/IAS.2006.256496, pp. 137–143, Oct. 2006.

Novel High Efficiency High Voltage Gain Topologies for AC-DC Conversion with Power Factor Correction for Elevator Systems

ABSTRACT:

Novel power factor corrected ac-dc rectifier topologies suitable for induction motor drive based elevator application are proposed. These converters make use of coupled inductor for power conversion and are capable of providing high voltage gain at low duty cycle and high efficiency. The current flowing through the coupled inductor is controlled through a feedback control loop to achieve unity power factor. The THD value of the current is observed to be approximately 4.8% which is within the limits prescribed by various standards. With the use of coupled inductor, the voltage stress of the switches operating at high frequency is reduced, which reduces switching losses. The loss comparison with the conventional converters shows a reduction of at least 22% of losses. The proposed scheme also results in reduction of the variable frequency drive’s dc link capacitance value as an ultra-capacitor bank is interfaced with the dc link through a bidirectional converter for improving efficiency and providing transient power requirements. This also helps in increasing the reliability and dynamic response of the system. The settling time for a step change in voltage reference is observed to be reduced by nearly 50%. Proposed topologies and schemes are validated through MATLAB/Simulink simulations and experiments.

KEYWORDS:

1.      Power Factor Correction

2.      Ac-dc conversion

3.      Single phase controlled rectifier

4.      Three phase controlled rectifier

5.      Reliability and ultra-capacitor

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1 Block diagram of an elevator system

EXPECTED SIMULATION RESULTS:

Fig. 2(a) Input current and voltage of the proposed1-ph rectifier system with PFC; (b)3-ph current for PFC operation of proposed rectifier configuration; (c) The dc link voltage step changes for 10μF and 500μF dc link capacitor; and (d) Ultra-capacitor current.

                           

CONCLUSION:

Novel AC-DC PWM rectifier topologies for 1-ph and 3-ph systems, based on high voltage gain dc-dc converter principle, were proposed, analyzed and validated through experiments and simulation studies. A major advantage of these topologies is that it is possible to achieve higher voltage gain at lower duty ratio. The operation symmetry is maintained. Input power factor correction is achieved. The use of coupled inductors enhances gain, but it also increases the ripple in the input current as the turns ratio is increased. Thus, there is a trade-off between the achievable gain and the ripple.

The losses of the proposed converter are compared with the conventional ac-dc converter, and it was observed that there is a reduction of about 22% losses. The losses estimated through experimental studies also reduced from 29W to 24W when the proposed topology was used. This shows a reduction of 17% losses in experiments. Therefore, the proposed converter gives higher efficiency than the conventional ac-dc converters. It was also observed that the use of an auxiliary storage reduced the dc link capacitance value from 500 μF to 10 μF for a 1-ph system. For the 3-ph system, the auxiliary unit can be used as a support during the grid voltage sag condition thereby reducing the dc link capacitance requirement. A low value of dc link capacitance not only helps in reducing the size and improving the reliability of system, but also in improving the dynamic response of the system.

The complete system was tested in hardware and the results were presented. A detailed description of the thought process behind the development of the proposed converter was also presented. The same thought process can be extended to the development of such converter topologies. The voltage stress on switch S2 and S3 reduces to 1/8th of its value as compared to the conventional topology. But, the value of peak current increases ‘n’ times. The increase in peak current increases the high frequency current ripple in the input side. However, the duty cycle is decreased with increase in the value of ‘n’. Therefore, the overall efficiency of the converter is increased.

The ac-dc topologies proposed in this paper are unidirectional. But, they can be made bidirectional by connecting a controllable switch across the diodes. This scheme is useful for the scenarios where the loads are regenerating. These bidirectional topologies can also be used as dc-ac converters to feed power into the grid. Thus, the scope of the proposed schemes is very wide and relevant.

REFERENCES:

[1] Ashok B.Kulkarni, Hein Nguyen, E.W.Gaudet, “A Comparative Evaluation of Line Regenerative and Non- regenerative Vector Controlled Drives for AC Gearless Elevators” 35th IAS Annual Meeting and World Conference on Industrial Applications of Electrical Energy, Rome, Italy: Institute of Electrical and Electronics Engineers Inc., Piscataway, NJ, Oct 2000, vol. 3.pp 1431 – 1437.

[2] "IEEE Std. 519", IEEE Recommended Practices and Requirements for Harmonic Control in Electric Power Systems, 1992.

[3] "IEC 1000-3-2 Int. Std.", Limits for Harmonics Current Emissions (Equipment Input Current16 A per Phase), 1995.

[4] "IEC 61000-3-4", Limitations of Emission of Harmonic Current in Low- Voltage Power Supply Systems for Equipment with Rated Current Greater than 16 A, 1998.

[5] J. Hahn, P. N. Enjeti and I. J. Pitel, "A new three-phase power-factor correction (PFC) scheme using two single-phase PFC modules," in IEEE Transactions on Industry Applications, vol. 38, no. 1, pp. 123-130, Jan/Feb 2002.

Virtual flux direct power control for PWM rectifiers based on an adaptive sliding mode observer

ABSTRACT:

 In the traditional virtual flux estimation for a three-phase PWM rectifier, the integration element causes problems for the initial value and DC bias, and the unstable grid voltage induces a non-constant flux amplitude. To address these issues, an improved direct power control (DPC) scheme based on an adaptive sliding mode observer (ASMO) is proposed in this work. The observer employs a sigmoid function as switch function to estimate the grid side source voltage. Meanwhile, an adaptive compensator instead of pure integral element is also designed to dynamically adjust compensation. The stability of this observer is proved by the Lyapunov function; moreover, simulations and experimental results indicate that this new virtual flux observer substantially improves the observation accuracy based on voltage sensorless control. The application of this strategy successfully suppresses the fluctuation of the dynamic voltage response in the DC bus, eliminating high-frequency noise from the grid side, whilst simultaneously boosting the power quality.

KEYWORDS:

1.       PWM rectifier

2.      Virtual flux

3.      Adaptive sliding mode observer

4.      DPC

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. System structure of traditional voltage sensor-less (VF-DPC)

EXPECTED SIMULATION RESULTS:

Fig. 2. Comparison of steady-state curve under four methods.

Fig. 3. Dynamic simulation I of saturation suppression and adaptive sliding mode.

Fig. 4. Dynamic simulation II of saturation suppression and adaptive sliding mode.

Fig. 5. Dynamic simulation of traditional voltage sensorless control.

Fig. 6. Dynamic simulation of adaptive sliding mode.

Fig. 7. Comparison of bus voltage during load step.

Fig. 8. Comparison of phase current and voltage during load step.

CONCLUSION:

This paper introduces sliding mode control in a virtual flux observer, based on the three-phase PWM rectifier model under virtual flux DPC; moreover, the systematic design of an orthogonal feedback compensation method to calibrate the flux estimation has been proposed. An improved sensorless control algorithm with an adaptive sliding mode observer has been simulated and experimentally verified. Results show that the combination of sliding control and virtual flux observer has improved dynamic response over traditional control strategies. This scheme can significantly improve the observation accuracy and dynamic response performance of the observer, and suppress the dynamic fluctuation and harmonic disturbance, increasing the overall power quality and delivery.

REFERENCES:

[1] J. W. Kolar, T. Friedli, J. Rodriguez, and P. W. Wheeler, “Review of three-phase PWM AC-AC converter topologies,” IEEE Transactions on Industrial Electronics, vol. 58, no. 11, pp. 4988–5006, Nov. 2011.

[2] Y. Zhang, Z. Li, Y. Zhang, W. Xie, Z. Piao, and C. Hu, “Performance improvement of direct power control of PWM rectifier with simple calculation,” IEEE Transactions on Power Electronics, vol. 28, no. 7, pp. 3428–3437, Jul. 2013.

[3] B. Singh, B. N. Singh, A. Chandra, K. Al-Haddad, A. Pandey, and D. P. Kothari, “A review of three-phase improved power quality ac-dc converters,” IEEE Transactions on Industrial Electronics, vol. 51, no. 3, pp. 641–660, Jun. 2004.

[4] A. Rahoui, A. Bechouche, H. Seddiki and D. O. Abdeslam, “Grid Voltages Estimation for Three-Phase PWM Rectifiers Control Without AC Voltage Sensors,” IEEE Transactions on Power Electronics, vol. 33, no. 1, pp. 859–875, Jan. 2018.

[5] A. Bechouche, H. Seddiki, D. Ould Abdeslam and K. Mesbah, “Adaptive AC filter parameters identification for voltage-oriented control of three-phase voltage-source rectifiers,” International Journal of Modelling Identification and Control, vol. 24, no. 4, pp. 319–331, 2015.

Variable Switching Frequency PWM Strategy of Two-Level Rectifier for DC-link Voltage Ripple Control

ABSTRACT

The switching frequency is an important control parameter of PWM rectifier to reduce switching losses and EMI noise. This paper proposed a variable switching frequency PWM (VSFPWM) strategy for DC-link voltage ripple control in two-level rectifier. DC-link voltage ripple is determined by the DC-link current directly, and can be predicted synchronously with PWM signals. A real-time prediction model of DC-link voltage ripple is derived for a common voltage oriented control (VOC) PWM rectifier. Then, VSFPWM control is introduced, which changes the switching frequency cycle to cycle with a restriction of DC-link voltage ripple peak value. Furthermore, the dynamic behavior is also observed when the proposed VSFPWM control scheme is adopted. Detail simulation and experimental comparisons are carried out between VSFPWM and normal constant switching frequency PWM (CSFPWM), which demonstrate the advantages of the proposed method.

KEYWORDS

1.      Voltage ripple

2.      Prediction

3.      Variable switching frequency

4.      PWM rectifier

5.      Switching losses

6.      EMI

SOFTWARE:  MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig.1 Control structure of AFE rectifier

EXPECTED SIMULATION RESULTS

Fig.2 Comparison between the prediction and the simulation results of the

DC-link voltage ripple in one line-cycle

Fig.3 DC-link voltage ripple comparison

Fig.4 Switching frequency comparison

Fig.5 AC-side current

Fig.6 Spectrum comparison (a) AC-side (2) DC-link

Fig.7 Step response (a) Step response of DC-link voltage (f) The change of

switching frequency with VSFPWM

CONCLUSION

The contribution of this paper is develop the VSFPWM strategy for DC-link voltage ripple control. Different from the previous work on the AC-side current ripple or torque ripple, the DC-link voltage ripple is nearly not affected by the PWM current ripple of AC-side. In a rectifier system, the DC-link voltage ripple is determined by the PWM method and load current, and the peak value of it is important for DC-link capacitor design or selection. The proposed VSFPWM fully utilizes the freedom of switching frequency, which is often neglected in the PWM module. However, the proposed VSFPWM is different from the random PWM [24], which changes the switching frequency based on the statistics and no prediction model is used. It should be noted that the proposed technique can be applied to a different power factor than the unitary one and not can be applied direct to the rectifier with neutral wire (four wire). Few conclusions can be derived as follows:

(1) DC-link voltage ripple prediction model can be built in the time-based-domain. With the three-phase duty cycles, AC-side current and load current measured by the current sensors, the DC-link voltage ripple peak can be predicted for updating the switching frequency in next cycle. The prediction method also applies to other PWM methods, and also be used for design and analysis of DC capacitors and DC battery reliability.

(2) In a whole line period, the switching frequency of VSFPWM continuously varies below the designed constant switching frequency, keeping the DC-link voltage ripple always under the requirement. Using the proposed VSFPWM strategy, the switching losses decrease significantly, and EMI noise reduces markedly.

(3) The dynamic property of VSFPWM is firstly investigated in a typical closed-loop control system. In fact, VSFPWM still has a good dynamic response, without nearly impairing the tracking performance shown in common CSFPWM. The open-loop Bode plot indicates the VSFPWM methods just decrease a little bit of bandwidth of both voltage control loop and the current in CSFPWM because of the reduction of average switching frequency.

REFERENCES

[1] J. Rodriguez, J. Dixon, J. Espinoza, J. Pontt, and P. Lezana, “PWM regenerative rectifiers: State of the art,” IEEE Trans. Ind. Electron., vol. 52, no. 1, pp. 5–22, Feb. 2005.

[2] B., Singh; B. N., Singh; K., Al-Haddad; A., Pandey; and D. P., Kothari,“A Review of Three-Phase Improved Power Quality AC-DC Converters,” IEEE Trans. on Industrial Electronics, Vol.51, pp.641–660, June 2004.

[3] A. Marzouki, M. Hamouda, and F. Fnaiech, “Sensorless Nonlinear Control for a Three-Phase PWM AC-DC Converter,” in Industrial Electronics (ISIE), 2010 IEEE International Symposium, Bari, Italy, pp. 1052-1057, July 2010.

[4] M.Malinowski, M.P.Kazmierkowski, andA.M.Trzynadlowski, “Acomparative study of control techniques for PWM rectifiers in ac adjustable speed drives,” IEEE Transaction on Power Electronics,vol.18,no.6,pp.1390–1396, Nov. 2003.

[5] Joerg Dannehl, Christian Wessels, and Friedrich Wilhelm Fuchs, “Limitations of Voltage-Oriented PI Current Control of Grid-Connected PWM Rectifiers With LCL Filters”, IEEE Transactions on Industrial Electronics, Vol.56, pp. 380-388, Feb. 2009.

Three-Phase Unidirectional Rectifiers with Open-End Source and Cascaded Floating Capacitor H-Bridges

ABSTRACT

This paper presents two topologies of three-phase semicontrolled rectifiers suitable for open-end ac power sources. The rectifiers are composed by a combination of two-level three phase bridges (controlled, semicontrolled or uncontrolled), and three single-phase floating capacitor h-bridges (controlled). These topologies generate two powered dc-links, each one belonging to a three-phase bridge. They present a reduced number of controlled power switches if compared to other open-end configurations of similar complexity found in the literature. It is also proposed a space-vector pulse width modulation (SV-PWM) approach and a method of floating capacitor voltage control dedicated to the topologies, with an equivalent approach based on the level-shifted PWM (LS-PWM). The proposed SV-PWM solving method is based on a redundant state selection (RSS) technique, which allows the floating capacitors voltage regulation. On the other hand, the LS-PWM solving method is based on the neutral voltage selection, which is shown to be equivalent to the SVPWM RSS technique seen from the control system. Simulation results are shown to validate proposed topologies, as well as the SV-PWM and LS-PWM techniques, and the control strategy. Experimental results are shown to demonstrate proposed configurations feasibility.

KEYWORDS

1.      Power electronics

2.      Ac-dc power conversion

3.      Unidirectional converters

4.      Cascade systems

5.      Multilevel systems

6.      Pulse width modulated power converters

7.      Space vector pwm

8.      Level shifted pwm

9.      Floating capacitor control

10.  Redundant state selection

SOFTWARE:  MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1: Proposed configurations with open-end power source and cascaded floating h-bridges. (a) Configuration 1, where converter A is a three-phase diode bridge. (b) Configuration 2, where converters A and B have semi-controlled legs.

EXPECTED SIMULATION RESULTS

Fig. 2: Simulation graphics for the conventional configuration 0. (a) Currents ik. (b) Voltages vk, vrk and v0s0. (c) Mean voltages vk, vrk and v0s0.

Fig. 3: Currents ik from simulation results for both proposed configurations with the LS-PWM. (a) For configuration 1. (b) For configuration 2.

Fig. 4: Voltages v1, vr1 and v0b0a from simulation results for both proposed configurations. (a) For configuration 1 with SV-PWM. (b) For configuration 1 with LS-PWM. (c) For configuration 2 with SV-PWM. (d) For configuration 2 with LS-PWM.

Fig. 5: Mean voltages v1, vr1 and v0b0a for both proposed configurations. (a) For configuration 1 with SV-PWM. (b) For configuration 1

with LS-PWM. (c) For configuration 2 with SV-PWM. (d) For configuration 2 with LS-PWM.

Fig. 6: DC capacitors voltages vCck from simulation results for both proposed configurations with the LS-PWM. (a) For configuration 1. (b) For configuration 2.

Fig. 7: Pole voltages va10a, vb10b, vcp10c1 and vcn10c1 for both proposed configurations. (a) For configuration 1 with SV-PWM. (b) For configuration 1 with LS-PWM. (c) For configuration 2 with SV-PWM. (d) For configuration 2 with LS-PWM.

CONCLUSION

In this paper, two configurations of unidirectional rectifiers were proposed. They were based on the cascaded connection of two three-phase bridges with three floating capacitor h bridges (one per-phase), which was allowed by the open-end configuration of the three-phase power source. The voltage regulation of the floating capacitor h-bridges was realized by two proposed PWM solving techniques. The first was applied to the SV-PWM, where methods for redundancy selection and state switching minimization were also proposed. The second was proposed for the LS-PWM as an alternative to the SVPWM. In this case, the floating capacitors voltage regulation was based in solving the PWM for appropriately selected neutral voltage references. Simulation results were provided to supply evidence that proposed topologies are viable and that proposed SV-PWM redundancy selection technique is effective within the control system. It was also shown that the control based on the LS-PWM was effective and equivalent to the SV-PWM. It could be concluded that the proposed configurations could present lower current THD and voltage WTHD with fixed switching frequency, as well as lower semiconductor losses with matched current THD, if compared to the conventional three-phase IBGT rectifier bridge. Experimental results were also provided to show the feasibility of proposed topologies and control strategy.

REFERENCES

[1] S. Debnath, J. Qin, B. Bahrani, M. Saeedifard, and P. Barbosa, “Operation, control, and applications of the modular multilevel converter: A review,” IEEE Transactions on Power Electronics, vol. 30, no. 1, pp. 37–53, Jan 2015.

[2] R. A. Krishna and L. P. Suresh, “A brief review on multi level inverter topologies,” in 2016 International Conference on Circuit, Power and Computing Technologies (ICCPCT), March 2016, pp. 1–6.

[3] F. Z. Peng, W. Qian, and D. Cao, “Recent advances in multilevel converter inverter topologies and applications,” in Power Electronics Conference (IPEC), 2010 International, June 2010, pp. 492–501.

[4] J. Rodriguez, J.-S. Lai, and F. Z. Peng, “Multilevel inverters: a survey of topologies, controls, and applications,” Industrial Electronics, IEEE Transactions on, vol. 49, no. 4, pp. 724–738, Aug 2002.

[5] M. Diaz, R. Cardenas, M. Espinoza, F. Rojas, A. Mora, J. C. Clare, and P. Wheeler, “Control of wind energy conversion systems based on the modular multilevel matrix converter,” IEEE Transactions on Industrial Electronics, vol. 64, no. 11, pp. 8799–8810, Nov 2017.