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.

A Multi-Input Bridgeless Resonant AC-DC Converter for Electromagnetic Energy Harvesting

ABSTRACT

Flapping electromagnetic-reed generators are investigated to harvest wind energy, even at low cut-off wind speeds. Power electronic interfaces are intended to address ac-dc conversion and power conditioning for single- or multiple-channel systems. However, the generated voltage of each generator reed at low wind speed is usually below the threshold voltage of power electronic semiconductor devices, increasing the difficulty and inefficiency of rectification, particularly at relatively low output powers. This manuscript proposes a multi-input bridgeless resonant ac-dc converter to achieve ac-dc conversion, step up voltage and match optimal impedance for a multi-channel electromagnetic energy harvesting system. Alternating voltage of each generator is stepped up through the switching LC network and then rectified by a freewheeling diode. Its resonant operation enhances efficiency and enables miniaturization through high frequency switching. The optimal electrical impedance can be adjusted through resonance impedance matching and pulse-frequency-modulation (PFM) control. A 5-cm×3-cm, six-input standalone prototype is fabricated to address power conditioning for a six-channel BreezBee® wind panel.

 KEYWORDS:

AC-DC conversion, electromagnetic energy harvesting, multi-input converter, resonant converter, wind energy.

 SOFTWARE: MATLAB/SIMULINK

 BLOCK DIAGRAM:

image001

image002

Fig. 1. Multi-channel EMR generators and PEI system: (a) conventional PEI; and (b) proposed multi-input PEI.

CIRCUIT DIAGRAM:

image003

Fig. 2. Illustrative scheme of the proposed multi-input converter (v(i)emf: EMF of #i reed; r(i)EMR: coil resistance; L(i)EMR: self-inductance; i(i)EMR: reed terminal current; v(i)EMR: reed terminal voltage; C(i)r1= C(i)r2: resonant capacitors; Lr: resonant inductor; Q(i)r1, Q(i)r2: MOSFETs; Dr: output diode; Co: output capacitor).

EXPERIMENTAL RESULTS:

image004

  •                                                             (a)
  • image005                                                                    (b)

Fig. 3. Experimental waveforms of power amplifiers: fin = 20 Hz; X-axis: 10 ms/div; Y-axis: (a) vemf = 3 Vrms; Ch1 = output voltage (Vo), 2.5 V/div; Ch2 = terminal voltage (vEMR) of reed #1, 10 V/div; Ch3 = input current (iEMR) of six reeds, 50 mA/div; and (b) vemf = 0.5 Vrms; Ch1 = output voltage (Vo), 0.5 V/div; Ch2 = terminal voltage (vEMR) of reed #1, 5 V/div; Ch3 = sum of the input currents (iEMR) of six reeds, 10 mA/div.

 image006                                                         (a)

image007

  •                                                           (b)

Fig. 4. Experimental waveforms of power amplifiers with step change: X-axis: 40 ms/div; Y-axis: (a) vemf = from 1 Vrms to 2 Vrms; Ch1 = output voltage (Vo), 1 V/div; Ch2 = terminal voltage (vEMR) of reed #1, 5 V/div; Ch3 = input current (iEMR) of six reeds, 50 mA/div; and (b) fin = from 20 Hz to 50 Hz; Ch1 = output voltage (Vo), 0.5 V/div; Ch2 = terminal voltage (vEMR) of reed #1, 5 V/div; Ch3 = input current (iEMR) of six reeds, 50 mA/div.

image008

(a)

image009

  •                                                                 (b)

Fig. 5. Experimental waveforms of EMR generators: X-axis: (a) 20 ms/div; (b) 100 ms/div; Y-axis: (a) constant wind speed; (b) wind speed step change; Ch1 = terminal voltage (vEMR) of reed #2, 5 V/div; Ch2 = output voltage (Vo), 1 V/div; Ch3 = terminal voltage (vEMR) of reed #1, 10 V/div; Ch4 = input current (iEMR) of reed #1, 10 mA/div.

 CONCLUSION

This manuscript introduces a multi-input bridgeless resonant ac-dc converter suitable for efficient, low-voltage, low-power, ac-dc power conversion of multiple electromagnetic generators. The multi-input single-stage topology is capable of directly converting independent, low-amplitude, alternative voltages of EMR inductive generators to a stepped-up dc output voltage with relatively high efficiency. Low-frequency alternating voltages of EMR generators are first converted into a high-frequency alternating voltage through an LC network and then rectified into a dc output voltage through a soft-switched diode. Optimal electrical impedance matching is achieved through proper LC network design and PFM control to scavenge maximum power of EMR generators. In addition, high-frequency soft-switching increases the potential of size miniaturization without suffering from switching losses. The converter performance is verified through a 5cm×3cm standalone prototype, which converts ac voltages of six-channel generators into a dc output voltage. A maximum PEI conversion efficiency of 86.3% is measured at 27-mW ac-dc power conversion. The topological concept, presented in this manuscript, can be adapted for rectification of any inductive voltage sources or electromagnetic energy-harvesting device.

REFERENCES

[1] A. Khaligh, P. Zeng, and C. Zheng, “Kinetic energy harvesting using piezoelectric and electromagnetic technologies – state of the art,” IEEE Trans. on Industrial Electronics, vol. 57, no. 3, pp. 850-860, Mar. 2010.

[2] Altenera Technology Inc., accessible online at http://altenera.com/products/.

[3] H. Jung, S. Lee, and D. Jang, “Feasibility study on a new energy harvesting electromagnetic device using aerodynamic instability,” IEEE Trans. on Magnetics, vol. 45, no. 10, pp. 4376-4379, Oct. 2009.

[4] A. Bansal, D. A. Howey, and A. S. Holmes, “CM-scale air turbine and generator for energy harvesting from low-speed flows,” in Proc. Solid-State Sensors, Actuators and Microsystems Conf., Jun. 2009, pp. 529-532.

[5] D. Rancourt, A. Tabesh, and L. G. Fréchette, “Evaluation of centimeter-scale micro windmills: aerodynamics and electromagnetic power generation,” in Proc. PowerMEMS, 2007, pp. 93-96.