Keisuke Kusaka

Experimental verification of rectifiers with SiC/GaN for wireless power transfer using a magnetic resonance coupling

This paper demonstrates that SiC and GaN diode rectifiers are used in a magnetic resonant coupling (MRC) for wireless power transfer system. The size of the resonance coils, which are used in the wireless power transfer using a MRC, depends on the transmission frequency. So, the MRC is desired to operate at a high frequency in the Industry Science Medical (ISM) band such as 13.56 MHz. In the receiving side, a rectifier which converts to the DC voltage from high frequency AC voltage is necessary to supply the power to the applications such as a battery charger for EV and home appliances. The experimental results show the maximum efficiency from a Radio Frequency (RF) power supply to DC outputs is 75.2% when the transmission distance is 150 mm. In addition, A power loss separation method of the wireless power transfer system is discussed in this paper. The experimental results verify the reflected power of the resonance coil which dominates the largest amount of the loss in the total loss. Therefore, the suppression of the reflected power is important for the wireless power transfer system using a MRC.

Isolation system with wireless power transfer for multiple gate driver supplies of a medium voltage inverter

In this paper, a multiple wireless power transfer system for multiple gate driver supplies of a medium voltage inverter is developed. The proposed isolation system achieves a galvanic isolation with an air-gap of 50 mm using a wireless power transfer with magnetic resonance coupling. It easily respects the standard of galvanic isolation, which is established by International electrotechnical commission (IEC). Moreover, the power is supplied from one transmitting board to six gate drivers without a solid magnetic core. In this paper, the isolation system is developed and tested. It is clarified that the isolation system transmits power of not less than 300 mW to each gate drivers beyond an air-gap. However, sum of the output power of the each receiving board are limited up to approximately 3.5 W because of a voltage drop in the equivalent series resistances of the transmission coils.

Proposal of Switched-mode Matching Circuit in power supply for wireless power transfer using magnetic resonance coupling

This paper discusses on the matching circuit in the power supply for wireless power transfer using a magnetic resonance coupling (MRC). The MRC is desired to operate at high frequency in the Industry Science Medical (ISM) bands such as 13.56 MHz. The resonance with high quality factor between the transmitting side and receiving side enables high efficiency for wireless power transfer. Therefore, the output frequency of the inverter must be aligned identically to the resonance frequency of the resonance coils in purpose of keeping the high transmission efficiency. In addition, the output impedance of the power supply has to be matched to the characteristic impedance of the transmission line that is despites to the output frequency. In this paper, the Switched-mode Matching Circuit (SMC) which operates to stabilize the output impedance of the inverter is proposed by the authors. The results confirmed in experimental and simulation demonstrates that, the SMC able to provide the variation of the output impedance.

DC to single-phase AC Voltage Source Inverter with power decoupling circuit based on flying capacitor topology for PV system

A novel power decoupling circuit using a flying capacitor topology is proposed in this paper. The inverters, which are connected to a single-phase grid, have single-phase power fluctuation at the twice the grid frequency. Thus, bulky electrolytic capacitor is generally used as DC link capacitor. In the proposed circuit, the power fluctuation is compensated by the flying capacitor in the flying capacitor DC-DC converter. The proposed circuit does not need an additional magnetic component in comparison with the conventional system, which has a boost chopper and an inverter. The proposed converter is experimentally tested with a 1-kW prototype. A voltage ripple at twice the frequency on the inverter DC voltage is suppressed from 35.1% to 4.6%. Moreover, the maximum efficiency of 94.5% with an output power of 1.0 kW is achieved. Finally, the design method of the boost-up inductor for proposed circuit is estimated by experiment. As a result, the error of the ripple current between design and measurement value is 4.7%.

Reduction on radiation noise level for inductive power transfer systems with spread spectrum focusing on combined impedance of coils and capacitors

Two reduction methods on radiation noise of inductive power transfer (IPT) systems are proposed and experimentally demonstrated. In the IPT systems for electrical vehicles (EVs) or plug-in hybrid electrical vehicles (PHEVs), noise reduction technologies are strongly required because the radiation noise from the IPT system for EVs or PHEVs must not exceeds the limits on standards; for example the regulation by CISPR is well-known regulation. The proposed method suppresses the radiation noise using spread spectrum technique. The radiation noise from the transmission coils of the IPT system is spread in a frequency domain by changing the output frequency of an inverter at random. The output frequency is selected according to pseudo random numbers. The first proposed method; a spread spectrum with a uniform distribution (SSUD), evenly selects the output frequency within 80 kHz to 90 kHz. Another method; a spread spectrum with a biased distribution (SSBD) is focusing on the output current of the inverter. The possibility for the select of output frequency is biased in proportion to a combined impedance of the transmission coil and the resonance capacitors. In the experiments with an output power of 3 kW, the fundamental components are suppressed by 42.6% and 72.1% by applying the SSUD and the SSBD in comparison with the conventional system, which operates the inverter at a fixed frequency.

Current source gate drive circuits with low power consumption for high frequency power converters

In this paper, three types of the gate drive circuits; voltage source, current source with continuous current and current source with discontinuous current gate drive circuits are compared from the view point of power consumption of the three types of the gate drive circuits and the switching loss of the main MOSFET. It is confirmed that the power consumption of the gate drive circuit is reduced by 56.4% using the current source gate drive circuit with discontinuous current source compared with that of the voltage source gate drive circuit by a switching test at the switching frequency of 1 MHz. Secondary, the switching loss of the main MOSFET is evaluated by experiment. The turn on and the turn off losses are 1.34 W and 1.76 W when the conventional voltage source gate drive circuit. On the other hand, the turn on and the turn off losses are 1.4W and 1.54W. The turn on loss and the turn off loss are almost same value because the input peak current of the conventional voltage source gate drive circuit and the input reactor peak current of the current source gate drive circuit with discontinuous current are same. Therefore, the current source gate drive circuit with discontinuous current can be used without increasing the switching loss of the main MOSFET similar to the conventional voltage source gate drive circuit. That is because the rise time and the fall time of the gate voltage on main MOSFET is same time.

Galvanic isolation system for multiple gate drivers with inductive power transfer — Drive of three-phase inverter

Medium-voltage motor drive systems, medium-voltage inverters, which have an input voltage and an output voltage of 3.3 kV or 6.6 kV, are widely used in industry applications. In the medium-voltage inverter, robust galvanic isolation among a control circuit and each gate drive supplies is required in order to drive high-voltage switching devices. In present, a transformer, which is designed to satisfy the safety standards, provides galvanic isolation. However, transformers prevent cost reduction of the isolation system. In this paper, the galvanic isolation system using only printed circuit boards are proposed. Moreover, a three-phase inverter is driven using the isolation system in order to confirm the utility of the isolation system. The proposed system transmits power from the transmitting board to six receiving boards using each transmitting coils made on the printed circuit boards. The air gap among the printed circuit boards assumes galvanic isolation. From the experimental results, it is confirmed that the three-phase inverter can be driven by the proposed galvanic isolation system.

Pattern design criteria of main circuit using printed circuit boards for parasitic inductance reduction

This paper investigates differences of parasitic inductances caused by DC bus bar patterns on printed circuit boards(PCB). The DC bus bar pattern on the PCB is limited depending on the layout of main circuits and the control circuits. Two patterns which are a laminated wiring pattern and a plane wiring pattern are compared in experiments and simulations. In this paper, it will be clarified that effects of the DC bus bars on PCBs such as a surge voltage of a switch in terms of the parasitic inductance depending on the circuits on PCBs. As a result, if the same parasitic inductance which is 20 nH, is realized between each wiring pattern at the same length, the plane wiring pattern requires over ten times of the pattern width compared with that of the laminated wiring pattern. Hence, the circuit size can be downsized when the laminated pattern is used. From the experimental results, the maximum surge voltage in the plane wiring pattern is larger than that in the laminated wiring pattern. In this case, the parasitic inductance value of the plane wiring pattern is three times that of the laminated wiring pattern. However, the surge voltage in the laminated pattern is reduced by 7% compared with the plane wiring pattern. As a consequence, the ratio of the surge voltage does not match that of the parasitic inductance. As a result, not only the parasitic inductance of the DC bus bar but also it is necessary to consider other parasitic inductances on PCBs such as parasitic inductances into input capacitors and the path between an upper MOSFET and a lower one and so on.

Experimental verification and analysis of AC-DC converter with an input impedance matching for wireless power transfer systems

This paper discusses the performance of an AC-DC converter which converts power from 13.56MHz AC to DC in a receiving side of wireless power transfer systems. The wireless power transfer systems are required to operate in high-frequency such as 13.56 MHz in order to achieve a high power density of transmission coils. Thus the AC-DC converter in the receiving side is demanded to operate at high-frequency. In such high-frequency region, the reflected power occurs when the input impedance is not matched to the characteristic impedance of the transmission line. In other words, the input impedance of the AC-DC converter needs to have the same impedance to the characteristic impedance of the transmission line. In order to overcome the problem, the AC-DC converter with an input impedance matching is proposed in this paper. The proposed AD-DC converter achieves the input impedance matching with a simple circuit configuration. It means that the converter can obtain sinusoidal input current and unity input power factor without a high-frequency switching except the diodes. In this paper, the impedance matching characteristics and the analysis of the operational modes of the proposed circuit are presented. The experimental results confirmed that the proposed converter enables a conversion from 13.56-MHz AC to DC with the sinusoidal input current. In this operation condition, the input impedance is 29.6 + j0.51 Ω. Because the design value of the input impedance is 50 + j0 Ω, there is a non-negligible error on the real part. This is attributed to the parasitic capacitances on the diodes. In order to solve this problem, an improved AC-DC converter is proposed newly. From experimental results, it achieves the input impedance of 52.7-j0.02 Ω. Besides, the reflection coefficient is suppressed by up to 94.5% compared with that of the conventional capacitor input-type diode bridge rectifier (CI-DBR).

Experimental verifications and desing procedure of an AC-DC converter with input impedance matching for wireless power transfer systems

An AC-DC converter with an input impedance matching for the receiving side of wireless power transfer (WPT) systems is mentioned in this paper. WPT systems are desired to operate in high frequency such as 13.56 MHz. In the high-frequency region, input impedance of the AC-DC converter on the receiving side of the WPT systems should be matched to the characteristic impedance of a transmission line because reflected power decreases the transmission efficiency of WPT systems. In this paper, the AC-DC converter with input impedance matching is experimentally demonstrated. Additionally, the design method of the proposed converter is described. First, the validity of the design procedure with using nondimensional parameters is confirmed with a simulation. Then, it is experimentally confirmed that the input impedance of the proposed converter is matched to the 50 + j0 Ω at a reflection coefficient of 2.6%. It means that, the reflection coefficient is significantly reduced by 94.5% compared with the conventional diode bridge rectifier (DBR) with a resistive load of 25 Ω.