A hybrid modulation strategy is proposed for the LCC - LCC compensated bidirectional wireless power transfer system ( LCC -BWPT), which aims to boost the efficiencies in the whole operating range. ...The basic operating modes of LCC -BWPT with the hybrid modulation strategy are analyzed, and the unified discrete-time model is then established based on the full-mode operation, which can accurately describe the state variables under all operating modes. Based on the model, the criteria for optimal operation are put forward in consideration of three working processes of LCC -BWPT, i.e., the constant current (CC) charging process, the constant voltage charging process, and the CC discharging process. The optimal control variables in three working processes are derived, respectively, which realize full zero-voltage switching operation and minimize the reactive current. On this basis, an optimal modulation strategy featuring high efficiency performance is proposed for LCC -BWPT. Besides, a control method independent of the real-time wireless communication is developed for LCC -BWPT with the optimal modulation strategy. Finally, a 1.2 kW prototype is applied, and experimental results verify the effectiveness of the proposed optimal modulation strategy, where the efficiencies are improved in the whole operating range.
Inductive power transfer (IPT) techniques are becoming popular in battery charging applications due to some unique advantages compared to the conventional plug-in systems. A high-performance IPT ...charger should provide the battery with an efficient charging profile consisting of constant charging current and constant charging voltage. However, with a wide load range, it is hard to realize the initial load-independent constant current (CC) and the subsequent load-independent constant voltage (CV) using a single IPT converter while maintaining nearly unity power factor and soft switching of power switches simultaneously. This paper systematically analyzed the characteristics of an LCC - LCC compensated IPT converter and proposed a design method to realize the required load-independent CC and CV outputs at two zero-phase angle frequencies. The design also combats the constraints of an IPT transformer and input voltage, thus facilitating the use of a simple duty cycle control operating at two fixed frequencies for both CC and CV operations. The design criteria, control logic, and sensitivities of compensation parameters to the input impedance and load-independent output are discussed. Finally, an IPT battery charger prototype with 1 A charging current and 24 V battery voltage is built to verify the analysis.
In this article, a self-tuning LCC/LCC wireless power transfer system based on switch-controlled capacitors is proposed to maintain a high power factor on the primary inverter side and fixed output ...power on the secondary side against self or mutual inductance variation of the magnetic coupler. The PI control on the primary side and the method of gradient descent on the secondary side are proposed based on the proposed normalized mistuned LCC/LCC circuit model. Only two switch-controlled capacitors on each primary and secondary side are used to implement the control scheme without the Wi-Fi communication or parameter identification. A 3 kW experiment setup was built in the lab and two different magnetic shields, namely ferrite and nanocrystalline, were tested on the secondary pad. According to the experiment results, the proposed system is proven to be able to maintain a high power factor (>0.9) and the desired dc output power against 52% mutual inductance variation and 12% self-inductance variation of the secondary pad. The proposed system can be applied as a wireless charger for electric vehicles or a high-power wireless charger test bench.
To achieve power and data synchronous transfer efficiently in the wireless power transfer system, a novel injection wireless communication method is proposed. Combined with the characteristic of the ...double-D coupling coil, the data are directly injected into one of the D coils and can be entirely coupled to the data receiving side and, therefore, the power lossless data transfer is obtained. Unlike traditional injection power and synchronous data methods, the additional wave trapper or trap inductor is not required with the proposed approach, and the power is delivered efficiently. The power transfer link and data transfer link are, respectively, analyzed, and the method to improve the data rate is proposed. Additionally, the interference between power and data delivery has been explored. The high-order harmonic interference with the data can be efficiently suppressed due to the low-pass filter characteristic of inductor--capacitor--capacitor ( LCC / LCC ) resonant composition topology, and the condition to eliminate the fundamental frequency power interference is proposed. A 150-W prototype is established to validate the performance of the proposed system. The experimental result indicates that the dc-dc power transfer efficiency reaches 90%, and the data rate is 166.7 kbps.
Compensation topologies play an essential role in wireless power transfer systems for electric vehicles. Specifically, the double-sided LCC compensated (DS- LCC ) topology has been widely adopted, ...owing to its inherent advantages, such as load-independent constant current (CC) output, low sensitivity to load variation, and high freedom in parameter design. However, large resonant devices in the DS- LCC topology lower the system efficiency and increase the complexity of optimal parameter tuning. Therefore, in this article, the parameters of the DS- LCC compensation topology are reconfigured by adjusting the ratios of its two compensation inductances without changing the specified system-level parameters, such as the loosely coupled transformer, operating frequency, and specified CC outputs. The system performance under each case is analyzed and compared in detail, based on which, an asymmetric parameter-design method is proposed to optimize the system efficiency. To verify the reasonability of the proposed tuning method, a 6.6-kW experimental prototype is configured, and comparative experiments are conducted. The experimental results indicate that, compared with the conventional method, the proposed parameter-tuning method improves the system efficiency under overall load conditions, especially under light loads.
In this article, an efficiency-oriented control strategy is proposed for LCC-LCC-compensated wireless power transfer (WPT) system to achieve zero-voltage-switching (ZVS) operation over a wide current ...regulation range, in which full-bridge (FB) and half-bridge (HB) modes are combined and switchable based on requirements from load. The harmonic-considered time-domain models for FB and HB modes are first built to calculate current through the switches at the turn- off moment accurately. Then, focused on the constant voltage charge stage with variable output current, the ZVS boundaries are identified in HB and FB modes as the preferable control trajectories, which determines the desired current output with joint considerations of frequency, phase-shift angle, and duty ratio. Next, a least squares optimization method is introduced to fit the theoretical control trajectories into a smooth curve that is practical for implementation on microcontrollers. Finally, a 4.4-kW WPT prototype is built to verify the feasibility and validity of the proposed control strategy. Results show that a high system efficiency can be achieved over a wide output current range, with an efficiency of 94.68% even at 20% rated power.
The LCC-LCC compensation is widely used in the inductive power transfer systems. However, there is no simple and accurate small-signal equivalent circuit model for this resonant converter. Based on ...the extended describing function method, this article proposed a full-order (17th-order) equivalent circuit model to accurately predict the small-signal behaviors. For simplification, the full-order model is gradually simplified to a ninth-order model and finally to a fifth-order model. The input to output transfer function are analytically derived for the first time. Both simulation and experimental results are presented to justify the effectiveness of the model, and the model is accurate up to one-fifth of the switching frequency.
Commutation failure (CF) is a frequent dynamic event at inverter of LCC-HVDC systems caused by AC side faults which can lead to inverter blocking, interruption of active power transfer, and even ...system blackout. To eliminate CFs and improve system performance, new Flexible LCC-HVDC topologies have been proposed in previous research but with limited analysis on its economic performance. Therefore, to further validate the applicability of Flexible LCC-HVDC topologies, this paper utilizes Life-Cycle Cost Analysis model to analyze the life-cycle cost of inverter stations for conventional LCC-HVDC, Capacitor Commutated Converter based HVDC (CCC-HVDC) topology and Flexible LCC-HVDC topologies including Controllable Capacitor based Flexible LCC-HVDC, AC Filterless Controllable Capacitor based Flexible LCC-HVDC and improved Flexible LCC-HVDC. Through a case study based on a 500 kV, 1000 MW LCC-HVDC scheme, comparison results show that the AC Filterless Controllable Capacitor based Flexible LCC-HVDC topology and the improved Flexible LCC-HVDC topology have lower cost than the conventional LCC-HVDC and CCC-HVDC topologies, which proves that the elimination of CFs can be achieved with reduced cost.
The characteristics of inductive power-transfer (IPT) systems are sensitive to the variation of the coupling coefficient caused by misalignment conditions or different gaps. This results in a ...reduction in transferred power and efficiency. The output characteristics considering frequency modulation applied in series-series (SS), inductor-capacitor-capacitor (LCC)-S and LCC-LCC compensated IPT systems have been explored, revealing that high-order compensation topologies hold limited power regulation ability if coupling varies significantly. The parameter sensitivity of LCC-LCC-compensated topology is investigated through the singular values (SVs) analysis. It is found that the variation of the parallel-compensated capacitors has the greatest impact on the output power. Aiming at alleviating the power drop caused by the coupling variation, a parameter offline tuning method realized by switching the parallel-compensated capacitance for a detuned LCC-LCC resonant converter is proposed for electric vehicle (EV) wireless charging. Analytical expressions have been derived in aiding the design of modified value of capacitance ensuring primary zero voltage switching (ZVS) operation. Thus, the detuned parameter combinations, which deliver rated power even with the worst coupling, are obtained. Finally, a 6.6-kw prototype has been built to verify the validity of the proposed topology, which can deliver 6.1 kW with an efficiency of 94% even when the coupling drops from 0.3 to 0.15.
Wireless power and data transmission (WPDT) is required in many scenarios. This paper proposes a novel WPDT scheme based on capacitive coupling. The power transfer is analyzed, and the power circuit ...is equivalent to a double-sided LCC compensated wireless power transfer system. The modulation, injection, extraction, and demodulation circuits for data transfer are introduced. The function of each element in the proposed system is explained in detail. In order to facilitate the design of a practical WPDT system, the specific steps are summarized. Theoretical analysis on the interferences between the power transfer and data transfer indicates that the interferences can be significantly diminished by proper design. A 100-W WPDT prototype is built. The measured power transfer efficiency, from dc input to dc output, is 90.5%. The transferred data are correctly recovered in the receiver side at a data rate of 119 kb/s. The data circuit works well even though the coupling coefficient is decreased by 60.2%. The practically measured interferences between the power transfer and data transfer are quite small. The power transfer and data transfer are not affected by these interferences.
