Received Date: September 12, 2016; Accepted Date: September 19, 2016; Published Date: September 26, 2016
Citation: Omori H, Ohara S, Kimura N, Morizane T, Nakaoka M (2016) A Novel Type of Wireless V2H System with a Bidirectional Single-Ended Inverter Drive Resonant IPT. J Electr Electron Syst 5: 200. doi: 10.4172/2332-0796.1000200
Copyright: © 2016 Omori H, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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Electric vehicles (EV) offer promise as an effective solution to environmental problems. One of the keys to their successful diffusion is the provision of adequate battery charging infrastructure. In order to create a charging infrastructure by installing equipment in such as locations as carports in private homes, the wireless battery charging system is very suitable. EVs can be used in smart house systems to supplement the energy storage. This vehicle to home (V2H) system essentially requires a bidirectional power transfer feature between the EV and home. This paper presents a new bidirectional inductive power transfer (IPT) system for wireless V2H with simplest components and low cost aiming at wide diffusion for home use. Proposed is a novel type of bidirectional wireless EV charging system with an efficient and compact type single-ended quasi-resonant high-frequency inverter for V2H.
Wireless; Charger; Bidirectional; Single-ended inverter; Home use; Power transfer; EV
In recent years, Electric Vehicles (EV) which are highly efficient as well as do not create air pollution, and offer promise as an effective solution to environmental problems with great advances of power electronic technology.
One of the key issues to their successful and wide diffusion is the provision of adequate battery charging infrastructure. In order to create a battery charging infrastructure by installing equipment in such as locations as carports in private homes, the inductive power transfer (IPT)-wireless battery charging system is indispensable for spread. The wireless battery charging system eliminates the use of power cables with plug. Merely by parking the car in a designated spot, the battery can be charged. It is a promising system for wider diffusion because it is easy and safe to use for a broad range of users including the elderly.
Usually as wireless EV charging power supply topologies have been half-bridge, push-pull, full bridge, boost half-bridge and boost fullbridge circuit configuration which have a plurality of power switching devices [1-4].
The authors have previously put into practice the cost-effective and high-efficiency single-ended quasi-resonant soft-switching inverter . Although EVs are primarily consider as a method of clean transport, they can also be used in smart house systems to supplement the energy storage. This vehicle to home (V2H) system essentially requires a bidirectional power transfer feature between the EV and home.
This paper presents a new system with the simplest components and low cost aiming at wide diffusion for home use. From a practical point of view, simple high-frequency inverter circuit topologies have to be effectively selected in accordance with specific cost effective applications. Proposed is a novel type of wireless EV charging system based on IPT technology with an efficient and compact type singleended quasi-resonant high-frequency inverter. The single-ended inverter, which can operate in the frequency range from 20-30 kHz under a self-excited ZVS control and its zero voltage crossing detector of resonant capacitor voltage is evaluated from an experimental point of view. Furthermore transfer power and efficiency have been successfully improved by pick-up circuit with resonant component. The output power of a proposed system is successfully improved by a resonant IPT circuit. EVs can be used in smart house systems to supplement the energy storage. This vehicle to home (V2H) system essentially requires a bidirectional power transfer feature between the EV and home. This paper presents a new bidirectional inductive power transfer (IPT) system for wireless V2H with simplest components and low cost aiming at wide diffusion for home use also. Proposed is a novel type of bidirectional wireless EV charging system with an efficient and compact type single-ended quasi- resonant high-frequency inverter for V2H. And a result of feasibility study by simulation and experiment is indicated for V2H .
An IPT-based wireless EV charging system is schematically illustrated in Figure 1. Figure 2 shows a proposed total system with a single-ended quasi-resonant high-frequency inverter. The system is mainly composed of a single-phase diode D1 rectifier with a L3-C3 filter, a single-ended quasi-resonant high-frequency inverter operating with a ZVS-PFM power regulation scheme in the frequency range of 20-30kHz, resonant capacitor C1 with the primary coil L1 which is loosely coupled to the pickup coil L2 as load side, a single-phase diode D2 rectifier with a L4-C4 filter connected with the battery bank of EV, and a specific power regulation control circuit due to the self-excited timing signal processing.
Operating principle of a proposed wireless EV charger
The periodic steady-state voltage and current operating waveforms of the single-ended quasi-resonant high-frequency inverter- fed DCAbstract DC converter in Figure 2 are illustrated in Figure 3, which include Mode I, II, III, IV, during one switching cycle.
Figure 4 illustrates switching-mode equivalent circuits in accordance with on-off operating mode due to the single active switch Q1 and passive switches in secondary-side diode bridge D2. The circuit state in which the active switch Q1 in the primary- side is cut off and passive switch D2 in the secondary–side is conducting is defined as Mode I and II (Figure 4a and 4b).
In Mode I (Figure 4a), when the active switch Q1 is turned off at t0, LC resonant tank circuit can operate. The inductor current and capacitor voltage become resonant state. Because of resonant operation, the voltage across the switch Q1 begins to increase sinusoidally from zero voltage. The active switch Q1 is turned off with ZVS (Zero Volt Switching) transition. The inductor current iL1, iL2 through the primary coil L1, the secondary coil L2 are decreasing. As soon as the inductor current iL2 reaches zero at t1, the state of D2 moves to Mode II shown in Figure 4b, the inductor voltage vL2 across the secondary coil L2 becomes –VC4 from VC4.
As soon as the resonant capacitor voltage reaches the supply DC voltage VC3 at t2, the voltage across Q1 becomes zero. At this point, the antiparallel diode of Q1 turns on naturally. The operating mode becomes Mode III shown in Figure 4c. The circuit state in which the active switch Q1 in the primary-side and passive switch D2 in the secondary-side are both conducting is defined as Mode III, IV (Figure 4c and 4d). The inductor current iL1 through the primary coil L1 and the active switch current iQ1 increase in a function time as illustrated in Mode III, IV of Figure 3 during Ton period.
When the secondly current iL2 reaches to zero at t3, the state of D2 moves to Mode IV shown in Figure 4d, and the secondary voltage vL2 changes to VC4 from –VC4. The active switch Q1 is turned off in accordance with its gate pulse duration time Ton
Judging from the operating voltage vQ1 and current iQ1 of the active switch, it is understood that the switch Q1 can achieve a soft -switching turn-on transition with ZVS. Note that the diode D2 in the secondary side can operate under a principle of ZCS (Zero Current Switching). As a result, the recovery current of D2 is considerably small, and switching power loss of D2 as well as switching noise can be minimized effectively. The active switch Q1 can achieve the complete soft switching transitions with ZVS at turn-on and turn-off. The synchronized PWM oscillator generates pulses synchronized with vL1 to achieve ZVS turn-on.
This system can supply an approximately constant current to battery owing to leakage inductance of wireless coupling planar coils without sensing any signals from the secondary-side pick-up coil circuit in EV.
Transfer-power improvement by a resonant pick-up Circuit equations of two planar spiral coils are given by
L1, L2: self-inductance of the primary-side power feeding coil and secondary side power receiving coil.
r1, r2: internal resistances of each planar coil.
K: electromagnetic coupling coefficient of two planar spiral coils.
M: mutual inductance between L1 and L2, which is influenced upon gap distance variable.
Output power of the system shown in Figure 2 is approximately represented by the following Equation:
VL1,VL2: effective voltages of the power feeding coil and the power receiving coil.
R0: equivalent resistance of the output circuit.
ω : operating frequency of the inverter.
On the other hand, output power Pr in the case of a power receiving coil L2 with a parallel connected resonant capacitor C2 is approximately represented as following equation:
Pr can be compared to Pnr as follows:
The resonant transfer power Pr is higher than the non-resonant transfer power Pnr under the condition of, then proposed is a resonant wireless EV charger with the pick-up side resonant capacitor in Figure 2 system .
Wireless coupling coil units
It is noted that the primary- side power feeding unit L1 is loosely coupled to the pick-up coil L2 of the secondary side power receiving unit for the battery charging power supply. In actual, these circular coils in the primary and secondary-side are assembled by the power litz wires in order to reduce power losses due to the skin effect. Two contactless planar and circular coil units with ferrite core sheets; power sending coil and power receiving coil are depicted in Figure 5.
We propose a power transfer configuration through a rear glass, because it is easy to install the pick-up unit. Then the diameter of coils is 170 mm, and the typical gap distance is 30 mm which include thickness of the rear glass and clearance.
As a matter of fact, some circuit parameters; mutual inductance M and magnetic coupling coefficient k of two planar spiral coils can depend upon the gap distance variable. Primary inductance L1 and secondary inductance L2 is not depending on gap (Figure 6).
The measured waveforms in a proposed EV charging system are shown in Figure 7. The active switch Q1 turn-on and turn-off by ZVS, and the self-excited ZVS control scheme well functions. In particular, in single-ended quasi-resonant inverter, note that the maximum voltage applied to the active switch Q1 becomes relatively high because of quasiresonant operation of primary side.
The measured value of output power in non-resonant case and resonant case vs. load characteristics for gap distance from 30 to 50 mm is shown in Figure 8. The output power with resonant pickup circuit is 1.5-2 times higher than that with non-resonant one. Measured power transfer efficiency is 90% under 30 mm gap in the resonant pick-up case.
A prototype of EV equipped with pick-up coil unit of the resonant IPT-wireless charging system and power feeding coil unit is shown in Figure 9a. The wireless charging system can charge 4.5 kWh in 5 hours as a feasibility study result as shown in Figure 9b.
A smart house with a vehicle to home (V2H) system is shown in Figure 10. Connected EV plays a role to supplement a storage battery system. As it is easy to connect EV the house by a wireless vehicle to home system, the EV is efficiently used for the smart house. The vehicle to home (V2H) system essentially requires a bidirectional power transfer feature between the EV and home. A new system configuration by a single-ended inverter with a resonant IPT circuit for bidirectional power transfer is shown in Figure 11. The proposed system is with simplest components and low cost.
In the EV charging mode, a home-side single-ended inverter produces high frequency power which is transferred to vehicle side circuit by resonant IPT as shown in Figure 12 left side. Capacitance C1 in home-side circuit operates as resonant capacitance for ZVS transition and capacitance C2 in vehicle-side circuit operates as resonant capacitance for resonant IPT. Input current IL3 smoothed by DC choke L3 is constant without ripple. Also output current IL4 smoothed by DC choke L4 is constant without ripple (Figure 12).
On the other hand, in the EV battery energy using mode, a vehicle-side single-ended inverter produces high frequency power which is transferred to home side circuit by resonant IPT indicated in Figure 12 right side. Capacitance C2 in vehicle-side circuit operates as resonant capacitance for ZVS transition and capacitance C1 in homeside circuit operates as resonant capacitance in power receiving for resonant IPT.
Figure 13 shows simulated operating waveforms of a proposed bidirectional circuit using a quasi-resonant high-frequency inverter in home to vehicle mode. The active switch SW1 is turned off and turned on with ZVS transition. And the active switch SW2 is kept off. A vehicle side circuit operates as a rectifier with a pick-up resonant circuit. This system operates as a resonant forward converter. Figure 14 shows operating modes of the bidirectional single-ended converter with resonant IPT in home to vehicle mode.
Figure 15 shows measured operating waveforms of proposed wireless V2H system. These waveforms are same as above mentioned simulation waveforms. The ZVS control scheme works well. Measured waveforms of vehicle to home mode also show the reverse operation scheme well function.
Figure 16a shows output power characteristics of home to vehicle mode. The output power decreases depending on gap distance, and can be controlled by conduction time TON. Figure 16b shows the output power characteristics in home to vehicle power transfer mode which same as those in vehicle to home mode.
Presented has been a new wireless EV charging system based on IPT technology with minimum components and low cost aiming at wide diffusion for home use. From a practical point of view, an efficient and compact type single-ended quasi-resonant high-frequency inverter was selected. The single-ended inverter which can operate in the frequency range from 20-30 kHz under a synchronized self-excited ZVS control and its zero voltage crossing detector of resonant capacitor voltage is evaluated from an experimental point of view. Output power of a proposed system has been successfully improved by a resonant IPT circuit. The output power with resonant pick-up circuit was 1.5-2 times higher than that with non-resonant one. Furthermore proposed has been a new resonant IPT wireless V2H system with a simplest and low cost bidirectional single-ended converter aiming at wide diffusion for home use also. And a result of feasibility study for V2H by simulation and experiment was indicated.