A High Power, High Quality Single-Phase AC-DC Converter for Wireless Power Transfer Applications Rahimi Baharom; Abd Razak Mahmud; Mohd Khairul Mohd Salleh; Khairul Safuan Muhammad and Mohammad Nawawi Seroji Faculty of Electrical Engineering Universiti Teknologi MARA Shah Alam, Selangor, Malaysia Abstract This paper presents a high power and high quality AC-DC converter for wireless power transfer (WPT) function. Based on the active power filter technique, the supply current waveform is forced to follow the desired reference signal, which is shaped to be continuous, sinusoidal and in phase with the supply voltage waveform. As a consequence, a low total harmonic distortion (THD) level can be achieved, with almost unity power factor, resulting in high quality power conversion system. This is performed by active power filter using the rectifier boost technique, which is piloted by a current control loop (CCL). Consisting of a subtraction circuit, proportional-integrator (PI) controller and comparator circuit, the CCL is carefully designed to enable the power factor corrector (PFC) function in the AC-DC converter. The half-bridge inverter that is driven by two power MOSFET is used to generate high-frequency alternating current (AC). Since both the transmitter and receiver coils, transmits and receives an AC voltage, respectively a high frequency full-wave diode-bridge rectifier is used to rectify the voltage into dc form to supply the dc loads. A proof-of-concept simulation model based on MATLAB/Simulink operating at 10kHz switching frequency is modelled and its performance is investigated. The selected simulation results are presented to verify the proposed converter. Keywords - AC-DC converter; wireless power transfer; power factor correction I. INTRODUCTION Nowadays, in line with increasing interest in WPT technology, many researchers focuses on developing various methods to enhance the WPT systems such as power transfer distance and efficiency [1] - [8] in order to improve their overall performance. A very important aspect of the system that need to be given a special focus is on designing the complete power converter for the WPT systems from an AC source. Conventional ac to dc converters, either in full-wave or half-wave operation, in emerging technologies such as WPT applications, are often inefficient due to the high THD level with low power factor. As a result, the amount of the output power would be reduced [9]. In order to solve the conventional AC-DC converters problems, an alternative method such as Class E resonant AC-DC converters that are known to operate efficiently at high resonant frequencies and at large input voltages, has been proposed. With a continuous, near sinusoidal supply current, which is in-phase with the supply voltage waveform, such method will lead to an improved overall system performance and increased efficiency, especially that of the transmitting coil driver. However, the use of class-e rectifier, requires the large inductance for the low-pass filter. In addition, the diode reverse voltage in the class-e rectifier is several times higher than the output voltage. As a result, these disadvantages may lead to the large size of the circuit configuration, hence, a high implementation cost [10]. Another drawback of the Class E converters is that their normal operation at open-loop has no feedback control to coordinate the precise soft switching operation [11]. This paper proposes to implement a high power quality AC-DC converter with WPT function. Here, an AC-DC converter with rectifier boost technique for power factor correction is developed for WPT systems to improve their performance and increase their overall system efficiency. Based on the well-established AC-DC converter with rectifier boost technique circuit configuration in [12] and [13], and WPT system in [14], this paper extends and enhances the work by integrating both circuit configurations to provide a more comprehensive power electronics converters for WPT systems. The paper is organized as follows. In Section II, the topology and operating principle of the AC-DC converter circuit to perform power factor correction will be introduced. The operating principle of the proposed high power quality AC-DC converter for WPT function will be explicitly described with the aid of corresponding timing and equivalent circuit diagrams. The CCL to drive active power switch to control the charging and discharging times of the boost inductor for power factor correction will be analytically investigated and presented. Then, the computer simulation model will be presented in Section III. Afterwards, the computer simulation results will be presented and discussed in Section IV. Section V gives the conclusions of the paper. DOI 10.5013/IJSSST.a.17.33.25 25.1 ISSN: 1473-804x online, 1473-8031 print
II. CIRCUIT TOPOLOGY AND OPERATING PRINCIPLE In this section, a high power quality ac to dc power converter with WPT function is presented as given in Figure 1. The advantageous features of this proposed converter include almost unity input power factor and low total harmonics distortion level hence, increase the overall performance of the proposed power converter system. extends to the receiver coil. The magnetic field then generates a current, which flows through the receiving coil. The ac current flowing through the receiver coil is converted back into dc form by the high-frequency full-wave diode bridge rectifier, which can then be used to power the dc load or device. The detail principle operation of WPT system have been researched and summarized in [14]. -Figure 1. The proposed high power quality AC-DC converter for WPT applications. Figure 1. The distorted supply current waveform The principle operation of overall system for high power quality ac to dc converter with WPT function can be summarized into four key steps as follows: The ac supply voltage is converted to the dc form using a full-wave diode-bridge rectifier. At this stage, a power factor corrector using rectifier boost technique is used to correct the highly distorted supply current waveform and result in a low input power factor drawn by diode-bridge rectifier and dc capacitor filter. In addition, the distorted supply current waveform as shown in Figure 2 has a rich high order harmonic content. This could lead to the emission of electromagnetic interference (EMI) that affects the operation of neighbouring system. By incorporating active power filter with the front-end ac to dc converter, efficient operation can be achieved, leading to a continuous, near sinusoidal supply current waveform with low total harmonic distortion level as shown in Figure 3. The principle of operation of ac to dc converter incorporating active power filter configurations that have been analyzed are summarized in [12] and [13] and the references therein. The output dc line voltage of the front-end ac to dc converter is then converted into the high-frequency ac form using a high frequency half-bridge inverter. The highfrequency ac square-wave output voltage waveform as shown in Figure 4, is then sent to the transmitter coil. The square-wave ac current which is flowing through the transmitter coil induces a magnetic field which Figure 2. The sinusoidal supply current and voltage waveforms of the front-end AC-DC converter with WPT function. III. COMPUTER MODELING MATLAB/Simulink circuit simulation software is used in this work to verify the system design. The simulated ac to dc converter incorporating the closed current control loop, high-frequency half-bridge inverter and WPT system are illustrated in Figure 5. Figure 6 shows the closed current control loop to perform as a power factor correction circuit. Table I shows parameters used in the modelling of the proposed converter. The chosen parameters are based on [12], [13] and [14] in order to investigate the behaviour of the proposed converter and for comparison purposes. Here, a rectifier boost technique is used to shape the distorted ac supply current drawn by the rectifier to be continuous, near sinusoidal and in phase with the ac supply voltage [15]. The proposed closed loop current controller consists of a DOI 10.5013/IJSSST.a.17.33.25 25.2 ISSN: 1473-804x online, 1473-8031 print
subtraction block set, proportional integral block set, comparator block set and carrier signal block set. The step response to control the reference signal is shown in Figure 7. Figure 6. The step response control of reference signal TABLE I. COMPUTER MODELING SCALE SIMULATION SYSTEM PARAMETERS System Parameters Supply voltage Active power filter switching frequency Values 40Vrms 10kHz Proportional controller gain 20 Integral controller gain 180 Half-bridge inverter switching frequency 20kHz Transmitter and receiver coils inductance 24µH Figure 3. The output DC voltage waveform of front-end AC-DC converter, the high-side and low-side PWM waveform and the square-wave output voltage waveform Figure 4. The top main model of high power quality AC-DC converter for WPT function Figure 5. The elements of current control loop Compensation capacitor 24µH Maximum Quality Factor, Q 80 IV. RESULTS AND DISCUSSION It can be seen that the typical converter without any filter function results in distorted supply current waveform as shown in Figure 8 with high THD level of 329.93%. The waveform is discontinuous with low power factor. The use of active power filter with rectifier boost technique shaping the discontinuous supply current waveform to become continuous, sinusoidal and in phase with the supply voltage waveform as illustrated in Figure 9. With the proposed compensation technique, the supply current waveform will follow the sinusoidal reference current waveform as shown in Figure 10. Hence, the THD level is reduced to 2.85%. Figure 11 shows the high frequency output voltage waveform of half-bridge inverter which is fed to the transmitter coil of WPT system, whilst Figure 12 shows the dc output voltage waveform for the proposed converter. Figure 13 and Figure 14 show the comparison results of the THD spectrum without any filter function and with the proposed compensation technique against the IEEE519 Standard respectively. By inclusion of the proposed compensation technique, the THD spectrum has been reduced well below the acceptable limit that was defined by IEEE519 Standard. As a result, the proposed converter will comply with the standard. Again, to verify the effectiveness of the proposed active power filter, a ±1A step response is used with varied value of the reference current. As clearly shown in Figure 15 and Figure 16, the supply current will follow the step change of the reference current for both during the reference values increased and decreased. DOI 10.5013/IJSSST.a.17.33.25 25.3 ISSN: 1473-804x online, 1473-8031 print
Figure 7. The distorted supply current waveform without any compensation filter Figure 11. The output DC voltage waveform Figure 8. The supply current and voltage waveforms using active power filter with rectifier boost technique Figure 12. The THD comparison of the distorted supply current waveform with IEEE519 Std Figure 9. The supply current and reference current waveforms using active power filter with rectifier boost technique Figure 13. The THD comparison of the supply current waveform after compensation with IEEE519 Std Figure 10. The output voltage waveform for controlled half-bridge inverter Figure 14. The step response of the supply current waveform with the reference current for IA step at 0.08 Iref increase DOI 10.5013/IJSSST.a.17.33.25 25.4 ISSN: 1473-804x online, 1473-8031 print
Figure 15. The step response of the supply current waveform with the reference current for IA step at 0.08 Iref decrease V. CONCLUSION A 10-kHz high power quality ac to dc converter for WPT system is demonstrated. With the use of rectifier boost technique, the converter is able to perform the function of WPT configuration by maintaining the high power factor operation and low THD level at the front-end of proposed converter. The simulation results prove that the proposed converter is able to achieve a high PF (PF > 0.997) and a low total harmonic distortion (THD) level of 2.85% for the supply current waveform. The distinctive features of this converter are favourable for future wireless dc power supply operating in the high power factor and low THD level. ACKNOWLEDGMENT Financial support from Institute of Research Management and Innovation (IRMI) Universiti Teknologi MARA Grant No: 600-IRMI/DANA 5/3/LESTARI (0015/2016) is gratefully acknowledged. REFERENCES [1] M. Kiani and M. Ghovanloo, The circuit theory behind coupledmode magnetic resonance-based wireless power transmission, IEEE Transactions on Circuits and Systems I: Regular Papers, vol. 59, no. 9, pp. 2065 2074, Sept 2012. [2] S. Cheon, Y. H. Kim, S. Y. Kang, M. L. Lee, J. M. Lee, and T. Zyung, Circuit-model-based analysis of a wireless energy-transfer system via coupled magnetic resonances, IEEE Transactions on Industrial Electronics, vol. 58, no. 7, pp. 2906 2914, July 2011. [3] Y.-H. Kim, S.-Y. Kang, M.-L. Lee, B.-G. Yu, and T. Zyung, Optimization of wireless power transmission through resonant coupling, in 2009 Compatibility and Power Electronics, May 2009, pp. 426 431. [4] N. Y. Kim, K. Y. Kim, J. Choi, and C. W. Kim, Adaptive frequency with power-level tracking system for efficient magnetic resonance wireless power transfer, Electronics Letters, vol. 48, no. 8, pp. 452 454, April 2012. [5] H. Jiang, B. Lariviere, D. Lan, J. Zhang, J. Wang, R. Fechter, M. Harrison, and S. Roy, A low switching frequency ac-dc boost converter for wireless powered miniaturized implants, in Biomedical Wireless Technologies, Networks, and Sensing Systems (BioWireleSS), 2014 IEEE Topical Conference on, Jan 2014, pp. 40 42. [6] E. Asa, K. Colak, M. Bojarski, and D. Czarkowski, A novel multilevel phase-controlled resonant inverter with common mode capacitor for wireless ev chargers, in Transportation Electrification Conference and Expo (ITEC), 2015 IEEE, June 2015, pp. 1 6. [7] Z. Yang, S. Kiratipongvoot, C. K. Lee, and S. S. Ho, A study of high-frequency-fed ac-dc converter with different dc-dc topologies, in Emerging Technologies: Wireless Power (WoW), 2015 IEEE PELS Workshop on, June 2015, pp. 1 8. [8] M. B. Shamseh, A. Kawamura, I. Yuzurihara, and A. Takayanagi, A wireless power transfer system optimized for high efficiency and high power applications, in 2014 International Power Electronics Conference (IPEC-Hiroshima 2014 - ECCE ASIA), May 2014, pp. 2794 2801. [9] S. Aldhaher, P. C. K. Luk, K. E. K. Drissi, and J. F. Whidborne, High input-voltage high-frequency class e rectifiers for resonant inductive links, IEEE Transactions on Power Electronics, vol. 30, no. 3, pp. 1328 1335, March 2015. [10] T. Nagashima, X. Wei, E. Bou, E. Alarcn, and H. Sekiya, Analytical design for resonant inductive coupling wireless power transfer system with class-e inverter and class-de rectifier, in 2015 IEEE International Symposium on Circuits and Systems (ISCAS), May 2015, pp. 686 689. [11] J. Tian, A. P. Hu, A. Abdolkhani, G. R. Nagendra, and S. Ren, A current-fed energy injection power converter for wireless power transfer applications, in Industrial Electronics Society, IECON 2013 39 th Annual Conference of the IEEE, Nov 2013, pp. 222 227. [12] R. Baharom, S. A. Ramli, and M. K. Hamzah, Peripheral interface controller (pic) based smart low power ac-dc converter, in Industrial Electronics Applications (ISIEA), 2010 IEEE Symposium on, Oct 2010, pp. 76 81. [13] R. Baharom, N. F. N. Ismail, N. R. Hamzah, and M. K. Hamzah, Studies on control electronics implementation of single-phase single switch active power filter, in Computer Applications and Industrial Electronics (ICCAIE), 2011 IEEE International Conference on, Dec 2011, pp. 144 149. [14] R. Baharom, M. K. M. Salleh, K. S. Muhammad, and M. N. Seroji, Impact of switching frequency variation to the power transfer efficiency of wireless power transfer converter, in 2016 IEEE Symposium on Computer Applications & Industrial Electronics (ISCAIE2016), 2016. [15] L. Junwei, C. Y. Chung, and H. L. Chan, Design and implementation of high power closed-loop ac-dc resonant converter for wireless power transfer, in 2014 IEEE 15th Workshop on Control and Modeling for Power Electronics (COMPEL), June 2014, pp. 1 8. DOI 10.5013/IJSSST.a.17.33.25 25.5 ISSN: 1473-804x online, 1473-8031 print