Power Electronics for Inductive Power Transfer Systems George Kkelis, PhD Student (Yr) g.kkelis13@imperial.ac.uk Sept 15
Introduction IPT System Set-Up: TX DC Load Inverter Power Meter ectifier
Wireless Power Transfer through Inductive Coupling Parallel esonance: Equations describing the Link: Inductive Link (1) link k TX ( 1 1 k TX ) v in,pa L TX L C LOAD () C LOAD k v in,pa Coupling Factor Series esonance: L TX Inductive Link L C LOAD (3) (4) par ser 1 k 1 k TX TX k Coupling Factor (5) L 3
ectification through Class-D and -E Topologies Advantages of Class-D Operation: Simple design; Low component stress regarding the required output voltage and current: Low conduction losses; Good utilisation of the diode; Switching losses can be minimized after proper selection of semiconductors; esistive input impedance if semiconductor parasitics are insignificant. Advantages of Class-E Operation: Presents a linear load to the inductive link: Current waveform with less harmonic content; Minimizes switching losses: Low rate of change of voltage during turn OFF; Semiconductor can reach higher switching frequencies; 4
Examined Topologies Half Wave esonant Class-E: Design Equations: L dc r M o dc V rect LOAD C r r 1 L r A o r Half Wave Class-D: Design Equation: dc LOAD Half Wave Class-E: Design Equations: dc Cd LOAD M I rect dc 5
Case Study: Test ig Class-D voltage driven inverter supplying power to the resonant tank and rectifier. Inverter output emulates induced emf in x coil. All the odd harmonics except the first are filtered by the series tuned coil, therefore the rectifier sees a current source at its terminals. Product of inverter s output voltage and output current is the input power to the x end. Input resistance is calculated using the measured power and input current. 6
Experimental esults: esonant Class-E Comparison between Class-E resonant rectifiers at 6.78-MHz, operating at and below resonance. 6 6 Operation below resonance more efficient with peak estimated 4 4 4 efficiency at 9% when 1-W were delivered to the dc load. Inverter Module (V) Inverter Module (V) Input impedance dependent on output voltage. The total harmonic distortion (THD) of the link s spectrum when utilizing the rectifier was calculated to verify the resistive nature of the topology: THD Time (sec) of generated x magnetic 1-7 Time (sec) field:.17%. Time (sec).55 35.5 3.56 41 6.5 4.5 1.57 5 7.5 5.5.58 63 8.5 16.5 3.59 1.57 49.5 7.5 4.5 1.58 5 38.5 5.5 13.59 6 1.5 49.5 6.5 4.5 1 7.55 7.5 35.5 8 3.5 68.5 6.5 4 9 4.5 79.5 57.5 1 5.5 8 Time (sec) x 1-7 x 1-7 Time (sec) Inverter Module (V) 6 4 ectifier Diode (V) -1 - ectifier Diode (V) -1 - -3-3 -3.55 35.5 3.5 1 6 1.5 41 6.5 4.5 1.57.55 7.5 5.5 3.58 3.5 63 8.5 16.5 43.59 1.5 4.5 74 9.5 7.5 54.5 1.5 5.5 85 38.5 65.5 13.5 6.5 96 1.5 49.5 76.5 4.5 7.5 1 7.55 87.5 35.5 8.58 3.5 69 8.5 6.5 49.5 9 4.5 1 79.5 57.5 1 5.5 8 Time (sec) Time (sec) x 1-7 Time (sec) Time (sec) Time (sec) x 1-7 x 1-7 x 1-7 Time (sec) Inverter Module (V) ectifier Diode (V) 6-1 - 7 )
Experimental esults: Current Driven Class-D and -E Current driven Class-D and Class-E were compared for IPT applications at 6.78-MHz when utilising Cree SiC diodes (C3D16A). Both rectifiers achieved their highest efficiency at high voltage operation, Class-D: 95% and Class-E: 9%. Junction capacitance of diodes introduced a frequency-dependent impedance in the Class-D and a small error in the required input resistance value of the Class-E. Class-D; Vertical: 5 V/div; Horizontal: 1 ns/div Class-E; Vertical: 1 V/div; Horizontal: 1 ns/div 8
Semiconductor Technology FET Transistors IXYS VISHAY CEE EPC GaN Systems Schottky Diodes CEE CEE NXP 9
Conclusions "Integration of a Class-E low dv/dt rectifier in a wireless power transfer system." Wireless Power Transfer Conference (WPTC), 14 IEEE. IEEE, 14. A rectifier design method was introduced with focus on maintaining the maximal efficiency of the IPT system. A voltage driven half-wave Class-E resonant rectifier was successfully integrated to an existing system verifying the design method. "Comparison of current driven Class-D and Class-E half-wave rectifiers for 6.78 MHz high power IPT applications." Wireless Power Transfer Conference (WPTC), 15 IEEE. IEEE, 15. Two rectifiers, current driven half-wave Class-D and Class-E, were compared for IPT applications at 6.78 MHz when utilising SiC diodes. A test circuit has been implemented for high frequency rectifier characterisation. 1