实现效率优化的无线电能传输系统双侧多周期不对称电压激励方法

Dual-Side Multi-Period Asymmetrical Voltage Excitation Control for Wireless Power Transfer System for Efficiency Optimization

在宽功率范围内实现高效功率传输是无线电能传输系统的基本要求。为提升全功率范围下无线电能传输系统的效率,该文提出了一种双侧多周期不对称电压激励方法。该方法在一、二次侧采用一种具有多个周期的不对称激励电压波形,当系统需要降功率运行时,根据功率大小对构成多周期激励电压波形的各个半周期脉宽依次进行缩减。同时,通过调节二次侧激励电压波形相对于电流波形之间的位置关系,实现宽功率范围内的开关器件零电压开通。通过各个半周期脉宽随功率降低依次缩减的变化模式,使激励电压相位差随功率的逐渐降低而出现多次回归至峰值的非单调变化特性,平抑了宽功率范围内激励电压相位差的波动幅度而将其维持于较高值,进而实现宽功率范围内的效率提升。实验结果表明,所提方法在宽功率范围内的效率不低于传统方法的效率,在大部分功率点的效率高于传统方法的效率。所提多周期不对称电压激励方法无需任何额外硬件电路,可在宽功率范围内实现效率提升。

Achieving high power transmission efficiency over a wide power range is the basic requirement of a wireless power transfer system.For inductive power transfer(IPT)systems with dual active full bridge structure,the conventional one-period(1P)asymmetrical voltage excitation control(AVC)method has achieved higher efficiency in comparison to the symmetrical dual-phase-shift(DPS)and triple-phase-shift(TPS)control method.To further improve the efficiency under a wide power range,this paper extends the conventional 1P-AVC method to multi-period AVC(MP-AVC)method for series-series compensated inductive power transfer(SS-IPT)system.By analyzing the SS-IPT system,it has been found that the power transfer efficiency of the intermediate resonant network depends on the ratio of the fundamental excitation voltages and the phase difference between them.The efficiency decreases when the fundamental excitation voltage ratio deviates from its optimal value or the phase difference deviates from 90°.To improve the power transfer efficiency of the intermediate resonant network while maintaining zero-voltage turning-on of the switches at the majority of the operating points,the asymmetrical excitation voltage waveform consisting of multiple periods has been proposed and used for both the primary side and the secondary side.When the system is needed to operate at a reduced power,the pulse width of every half period that composes the multi-period excitation voltage waveform is decreased sequentially according to the power amount.And the relative position of the excitation voltage waveform to the current waveform is also adjusted to achieve wide-power-range zero-voltage turning-on for the power switches.The primary-side and secondary-side excitation voltage waveforms are also controlled to keep the voltage ratio close to the optimal voltage ratio for higher efficiency.By utilizing the sequentially-decreasing variation pattern of the half-period pulse width with the reduction of power amount,the non-monotonic variation characteristic of the excitation voltage phase difference periodically returning to its peak value for multiple times can be achieved,which smooths out the fluctuation magnitude of the excitation voltage phase difference and maintains the excitation voltage phase difference at a high value,increasing the maximum achievable phase difference under the constraint of zero-voltage turning-on of all switching devices,and can lead to efficiency improvement in a wide power range.The experiment results has shown that the efficiency curves of the proposed 2P-AVC and 3P-AVC method have a multi-peak characteristic,and the number of peaks increases with the increasing of the number of periods.The efficiency achieved with the proposed two-period and three-period AVC(2P-AVC and 3P-AVC)method is equal to or higher than the efficiency achieved with conventional DPS,TPS or 1P-AVC method over the full power range,especially at light-loading conditions.The rated power of the experiment platform is 3.7 kW.At the coupling coefficient of 0.2,the efficiency with 2P-AVC is 92.6%at a light loading condition about 130 W,which is 3 percentage points higher than that with 1P-AVC.At the coupling coefficient of 0.1,the efficiency with 2P-AVC is 85%at about 85W,which is 8 percentage points higher than that with 1P-AVC.Besides,the zero-voltage turning-on is achieved with the proposed control method.The multi-peak efficiency curve characteristic obtained from the experiment has verified the periodical-returning characteristic of the phase difference with the varying of power,which smooths out the power transfer efficiency in a wide power range.The proposed MP-AVC method does not require any additional hardware circuits and can significantly improve the overall efficiency especially at light-loading conditions.