PowerWoW technology dedicated its accumulated research and practical experiences in finding new resonant circuit structures and their associated control techniques to improve the fundamental characteristics of the WPT system.
The targeted areas including: novel tuning circuits for both Tx and Rx, closed-loop dynamic control techniques, and reducing reflected effects of Rx onto Tx system for lowering the control effort of Tx.
The development of novel tuning circuits is aiming to provide a variably controlled voltage source at the output of the Rx so as to fulfill the load requirements. This particular feature can provide a constant voltage at the output regardless of the load variations, which is a feature desired in most of the applications. The novel tuning circuit would also be capable of boosting the insufficient output voltage, which may be caused by low coupling between Tx and Rx, by autonomously adjusting its voltage boosting capability. This is achieved by using feedback signals of voltage and current waveforms from both AC and DC side of the Rx as the inputs of a controller, and based on the studied input-output behaviors of the circuit to thereby tuning the resonant circuit for maintaining the resonance of the system.
Associated closed-loop control would also be developed to assist the novel tuning circuit for achieving the following control objectives, such as:
1. By using the feedback signals and the studied input-output behaviors of the system to perform dynamic tuning of the system for maintaining system resonance while boosting the output voltage to a desired level.
2. Compensating for system parameter variations, for example, operating frequency variations and component manufacturing tolerances.
3. Optimization of system performance in multiple-pickups systems.
Different from the radio frequency (RF) systems where the antenna and the circuit impedance matching design is mainly based on the assumption of Tx and Rx has a fairly long operating distance which in most of the cases the reflected impedance from the Rx side can be regarded as negligible, in the WPT systems, the reflected effects of Rx side to the Tx may be quite significant especially when the two sides are closely coupled. This results the matching at Tx side becomes complicate and may require the capability of dynamic matching due to the Tx and Rx can have a variable coupling distance if the user scenario is allowed. This may raise two technical problems that need to be solved which are the appropriate matching circuit selection and the dynamic tuning techniques of it. PowerWoW therefore focuses on the development of the matching circuit design which best suited for the novel tuning circuit, and also concentrated on the potential control techniques on the dynamic tuning such as using techniques that has been previously adopted in power system PFC using switching inductor/capacitor. This method may improve the system performance by smooth tuning control.
To conclude the core competencies of PowerWoW, our strength is focused on solving some of the fundamental issues that existed in the present WPT system through a novel resonant circuit design to include the desired circuit characteristics and thereby improve the system performance fundamentally.
These competencies include:
1. To provide a constant voltage at the output of Rx regardless of the load variations.
2. To provide a controllable output voltage boosting capability for Rx in response to possible coupling variations.
3. To provide a closed-loop control for the compensation for practical system parameter variations such as operating frequency and component manufacturing tolerances.
4. To maintain the resonant condition of the WPT system for achieving better power transfer capability and efficiency.
Advantages of these competencies can be further elaborated as follow:
- The ability to provide a constant output voltage allows a simpler design on the output regulation of Rx which typically is a buck converter. Since the efficiency of a buck converter can generally be determined by the potential difference between its input and output, by having a constant output voltage close to the desired value can therefore obtain a better output conversion efficiency. This not only improves the system performance but may also lower the complexity and thus the cost of the buck converter.
- In order to obtain sufficient input voltage on the Rx coil through the magnetic induction to the Tx coil and thereby maintain the output voltage at a desired level, the Rx coil is generally chosen to have a fairly large dimension for such a purpose. However, with a controllable output voltage boosting capability, the size of the coil may be less concerned since the output voltage may be boosted to a sufficient level if needed. This feature practically introduces the spatial freedom to WPT system as the output voltage can be dynamically adjusted according to the load demand regardless of the coupling variations of the system, in addition, the size of the Rx coil may be reduced while still being able to maintain the output voltage at a desired level, which the feature not only improves the system performance but may also reduce the cost on the Rx coil design.
The developed closed-loop control compensates the system parameter variations which often occur in a practical WPT system. As the WPT system requires the system to be fully resonant at all times for the expected system performance, which in fact is difficult to be maintained in practice, the closed-loop control using the obtained voltage and current waveforms within the resonant tank will allow the system to have a higher tolerances in the system parameters, making mass production of such a system more feasible with lower BOM costs due to the ease on component selections.