Mariusz Bojarski

A Novel Phase-Shift Control of Semibridgeless Active Rectifier for Wireless Power Transfer

A novel phase-shift control of a semibridgeless active rectifier (S-BAR) is investigated in order to utilize the S-BAR in wireless energy transfer applications. The standard receiver-side rectifier topology is developed by replacing rectifier lower diodes with synchronous switches controlled by a phase-shifted PWM signal. Theoretical and simulation results show that with the proposed control technique, the output quantities can be regulated without communication between the receiver and transmitter. To confirm the performance of the proposed converter and control, experimental results are provided using 8-, 15-, and 23-cm air gap coreless transformer which has dimension of 76 cm × 76 cm, with 120-V input and the output power range of 0 to 1kW with a maximum efficiency of 94.4%.

Frequency-Dependent Resistance of Litz-Wire Square Solenoid Coils and Quality Factor Optimization for Wireless Power Transfer

In order to achieve the highest efficiency of wireless power transfer (WPT) systems, the quality factor of the resonant coil should be as high as possible. Due to the skin effect and the proximity effect, the coil resistance increases with the increase in the frequency. The highest quality factor exists for the optimal frequency together with the corresponding frequency-dependent inductor resistance. This paper employs the Biot-Savart law to calculate the magnetic field strength, which results in the proximity-effect resistance in single-layer litz-wire square solenoid coils without a magnetic core. A strand-number coefficient is introduced to reflect the influence of the strand number inside the wire bundle on the proximity-effect resistance. The coefficient is obtained through simple inductor resistance measurements for various numbers of litz-wire strands. The optimal frequency for the highest quality factor is derived based on the resistance evaluation. Several prototype coils were manufactured to verify the resistance analysis. Two 50 cm × 50 cm square coils were employed to construct a WPT prototype. The maximum dc-dc efficiency of this WPT was about 75% at 100-cm distance.

A novel phase control of semi bridgeless active rectifier for wireless power transfer applications

A novel phase control of a semi-bridgeless active rectifier (S-BAR) is investigated in order to utilize the S-BAR in wireless energy transfer applications. The standard receiver side rectifier topology is developed by replacing rectifier lower diodes with synchronous switches controlled by a phase-shifted PWM signal. Theoretical and simulation results show that the performance of the proposed S-BAR is appropriate for resonant converters that require power control at the secondary side such as contactless energy transfer systems. To confirm the performance of the proposed converter and control, experimental results are provided for a 1 kW prototype using 3, 6, and 9 inches air gap coreless transformer, which has dimension 2.5 by 2.5 feet, with 120 V input and the output voltage range of 0 to 95 V with a maximum efficiency of 94.4%.

A constant resistance analysis and control of cascaded buck and boost converter for wireless EV chargers

This paper presents a new constant resistance control technique for a cascaded buck and boost converter, which is suitable for wireless energy transfer pickup systems in variable load applications such as battery or ultra-capacitor charging. In order to achieve high efficiency, an impedance matching network is commonly used in the contactless energy transfer systems especially for low coupling coefficient circuits. The proposed control technique avoids a divergence of the designed impedance matching system considering the load variation. This is important to secure high wireless energy transfer efficiency under voltage and current changes at the load terminals. The transfer function of the converter is presented with theoretical calculations describing the small-signal model. The system model is used to control the resistance in the cascaded buck and boost converter for electric vehicle (EV) charging applications in a 2 kW prototype.

Asymmetrical Duty-Cycle and Phase-Shift Control of a Novel Multiport CLL Resonant Converter

In this paper, a novel multiport CLL resonant converter with a phase shift and asymmetrical duty-cycle control is analyzed. The power flow can be maintained with the phase shift between ports, whereas the asymmetric duty cycle manages the output voltage at the load terminals. Series connected transformers at the secondary side enable to split the power in each port and reduce the voltage stresses on the switches compared with the parallel connected transformers. Even under the unbalanced input conditions, the power flow between ports can be managed by the central control without any need for communication devices. In order to investigate the power distribution in each port, two different isolated dc sources and a variable load are used. The converter operation is tested at 40, 80, or 120 V inputs, with the output of 200 V at a full power of 1 kW with a maximum efficiency of 97.4%. The experimental results show that the multiport CLL resonant converter with the proposed controller is an appropriate topology for sustainable energy platforms, which are supplied by different types of energy sources, such as photovoltaic, fuel cell, wind, and so on, at various power capacities.

Effect of wireless power link load resistance on the efficiency of the energy transfer

With the proper impedance matching system, a high efficiency can be acquired in wireless power transfer applications. Variations of the coupling coefficient factor could deviate, however, the impedance matching system from the designed considerations. In this paper, the transmitter reflected impedance from the receiver side is analyzed to avoid divergence of the impedance matching network considering a wide air gap range between transmitter and receiver sides. A 2 kW contactless system is designed to investigate an optimum impedance requirement by testing several displacement gaps between coils. Experimental results are demonstrated to reveal a relation between the efficiency and the reflected impedance.

Analysis and Control of Multiphase Inductively Coupled Resonant Converter for Wireless Electric Vehicle Charger Applications

In this paper, an inductively coupled multiphase resonant converter is presented for wireless electric vehicle charging applications. As an alternative to the traditional frequency and phase shift control methods, a hybrid phase-frequency control strategy is implemented to improve the system efficiency. A theoretical analysis of the proposed system is carried out considering a wide battery state-of-charging range. In order to confirm the proposed converter and control technique, a laboratory prototype wireless charger is designed using 8-in air-gap coreless transformer and rectifier. The proposed control is compared with the conventional control methods for various load conditions at the different power levels. In comparison results, the proposed hybrid control methodology demonstrates the efficiency improvements of 1.1% at the heaviest load condition and 5.7% at the lightest load condition.

A 25 kW industrial prototype wireless electric vehicle charger

A 25 kW wireless charger design for electric vehicles is presented in this paper. The wireless charger consist of three phase power factor corrector (PFC), three phase resonant inverter, primary and secondary coils with series resonant compensation, and a rectifier. In the proposed design, PFC provides a constant voltage DC Bus and the whole output regulation is done by the resonant inverter. It simplifies the rectifier structure to the simple full-bridge topology. The design is verified with experiments at the output power from 0 W to 25 kW. The measured system efficiency was up to 91%.

A novel multi-level phase-controlled resonant inverter with common mode capacitor for wireless EV chargers

A novel multi-level phase-controlled resonant inverter is presented in this paper. The inverter is intended for wireless energy transfer systems. The proposed converter topology is obtained with two identical multi-level dc-ac inverters, connected in parallel through two common-mode capacitors. To overcome high voltage and current stresses across the switches, the proposed topology splits the voltage and current in each phase so that high power applications are possible with the proposed converter. An asymmetrical phase-shift modulation with a constant frequency regulates the output voltage in order to overcome the drawback of a wide range of operating frequency that occurs in conventional wireless power topologies. Theoretical and simulation results of the proposed circuit show that the converter performance is suitable for high power contactless electric vehicle (EV) chargers. The performance of the proposed converter is confirmed with experimental results using 8 inch air gap coreless transformer, which has dimension 2.5 by 2.5 feet. The converter is tested at 120 V input with the output of 120 V at a full power of 1 kW with a maximum efficiency of 93.7%.

A novel LLC resonant converter with semi bridgeless active rectifier

A novel LLC resonant converter with semi bridgeless active rectifier (S-BAR) is proposed in this paper. The presented secondary side rectifier topology is applicable for EV battery chargers with wide output voltage range. This topology is achieved by replacing rectifier lower diodes with synchronous switches and regulation by a phase-shifted PWM signal. Simulation results show that the performance of the proposed S-BAR is appropriate for LLC resonant converter and EV battery charger applications. To confirm the performance of the proposed converter experimental results are provided for which output voltage range of 0 to 80 V with an input of 120 V and the full power 600 W.