Opportunity
Wireless power transfer (WPT) systems, especially those employing active rectifiers, require precise frequency and phase synchronization between the primary-side inverter and the secondary-side rectifier to achieve high efficiency, zero-voltage switching (ZVS), and continuous power regulation using advanced controls like triple-phase shift (TPS). Existing synchronization methods suffer from critical limitations. Real-time communication techniques (e.g., Wi-Fi) introduce milliseconds of delay and are susceptible to electromagnetic interference in high-power operation, making them unreliable. Zero-crossing detection (ZCD) methods use additional coils or counters but are sensitive to system detuning, harmonics, and coil misalignment, as the assumed phase relationship often fails when the resonant tank is detuned. Other methods that sample and process the secondary current require complex computations, current/voltage sensors, and still cannot achieve arbitrary phase differences needed for TPS. Some approaches add bulky auxiliary coils and inverters, increasing cost and complexity. Consequently, there is a pressing need for a synchronization technique that is robust against detuning, harmonics, and misalignment, can achieve arbitrary phase differences, and uses simple, low-cost hardware without real-time communication.
Technology
The invention introduces a synchronization method based on detecting voltage transients on a sensor inductor connected to the secondary-side resonant tank. In a series-series (S-S) compensated WPT system, when the inverter switches change state, the inverter output voltage undergoes a sudden step. This transient propagates through the coupled coils and induces a voltage spike on the sensor inductor, which is placed in series with the secondary coil. The sensor inductor can be implemented as a small magnetic ring (e.g., nickel-zinc ferrite with a permeability of 100 and 22 turns) to provide electrical isolation and a measurable signal. The voltage transients are first filtered using a notch filter (centered at the switching frequency) or a high-pass filter to enhance the transient features by attenuating the fundamental component. The filtered signal is then sampled by a high-speed ADC and processed by a controller on the secondary side. By ignoring voltage transients caused by the rectifier's own switching (using a short time window around known rectifier switching instants), the controller detects the inverter's rising and falling edges from the remaining transient pulses. Using counters, the switching period and the inverter's duty cycle (α) are determined, and a delayed counter is generated to produce the rectifier driving signals with the desired phase shift (θ). This process achieves phase and frequency synchronization within one or two switching cycles (less than 25 μs), independent of system detuning or current harmonics. The method requires only a magnetic ring, a sampling module, a filter, and a conditioning circuit—no bulky coils, current sensors, or communication links.
Advantages
- Robustness against system detuning: Works reliably even when the resonant frequency shifts (e.g., from 85 kHz to 80 kHz or 90 kHz), as the method relies on transient detection rather than zero-crossing assumptions.
- Fast synchronization: Achieves synchronization within one or two switching cycles (<25 μs), significantly faster than communication-based or PI-controller methods (which can take milliseconds).
- Simple hardware: Requires only a small magnetic ring (sensor inductor), a notch/high-pass filter, a sampling circuit, and a signal conditioning circuit—no additional coils, current sensors, or wireless modules.
- Low computational load: The detection and control algorithm is straightforward, using edge detection and counters rather than complex Fourier transforms or PI loops.
- Immunity to harmonics: The filter suppresses fundamental harmonics, making transient detection unaffected by harmonic distortion.
- Supports arbitrary phase differences: Works with TPS and other multi-phase-shift controls, enabling full efficiency optimization and ZVS.
- Minimal power loss: The sensor inductor’s series inductance (~70 nH) introduces negligible losses; magnetic ring temperature rise is minimal even at 4A.
- Wide coupling range: Functional for coupling coefficients as low as 0.13 (weak coupling) and robust for stronger coupling.
Applications
- Electric vehicle wireless charging: Both stationary and dynamic charging systems benefit from reliable synchronization under varying coupling and detuning.
- Consumer electronics: Wireless chargers for smartphones, laptops, tablets, and wearable devices requiring high efficiency and compact design.
- Medical implants and devices: Safe, interference-free wireless power delivery for implantable sensors, pacemakers, and neurostimulators.
- Industrial robotics and automation: Contactless power transfer for rotating or moving parts in manufacturing lines.
- Underwater and harsh environments: Where wired connections are impractical and communication is unreliable.
- Bidirectional WPT systems: Enabling vehicle-to-grid (V2G) and other bidirectional energy transfer applications.
