To regulate the output voltage of inductor–capacitor–capacitor-series ( LCC -S) compensated wireless power transfer (WPT) system, a hybrid control strategy of phase shift modulation (PSM) and a switch-controlled capacitor is presented in this article. In the proposed hybrid control strategy, LCC -S compensated WPT system can realize wide output voltage regulation with zero voltage switching (ZVS), and the reactive current in a resonant tank can be minimized in the whole voltage range. Besides, the current in the primary coil of LCC -S compensated WPT system can be regulated with PSM, which helps to reduce the power loss of the primary coil at light load. Compared with conventional dual-loop hybrid control, the proposed hybrid control can regulate two control variables with one feedback loop simultaneously. To verify the theoretical analysis, a 500-W prototype with 400-V input voltage, 100−250-V output voltage is built. The experimental results show that the inverter can realize ZVS within the whole voltage range and a peak efficiency of 94.7% can be obtained.

A LCC-S compensated wireless power transfer (WPT) system with dual decoupled receive coils and a cascaded PWM regulator is proposed in this paper. The dual decoupled receive coils, comprising of bipolar coil and unipolar coil, provide two power paths. Most of input power is transferred to load directly through bipolar coil while only small portion of input power is transferred through unipolar coil and the cascaded PWM regulator, which can reduce power loss effectively. The output voltage of WPT system is regulated by the cascaded PWM regulator, thereby wireless communication links (WCLs) is not required in the feedback control loop, which leads to simple control circuits and good stability. Compared with conventional WPT system with two-stage power conversion, it is cost-effective as voltage/current stress of PWM regulator can be significantly alleviated. Besides, the LCC-S compensated WPT system can operate under zero phase angle (ZPA) condition with low voltage-ampere rating components. A 1.5kW prototype is built and experimental results show that the system efficiency up to 93% can be achieved under full load, which is 2.3% higher than that of conventional WPT system with two stage power conversion.

Usually, the inductance of transmitter coil is sensitive to misalignments of the magnetic coupler when the asymmetrical coil structure with a smaller size receiver coil is adopted. The fluctuation of the inductance of transmitter coil will increase the power losses in the primary inverter. To compensate the fluctuation of the transmitter coil inductance, a digital switch-controlled capacitor (D-SCC) for maximum efficiency point tracking (MEPT) of LCC-S compensated IPT system is proposed. Consequently, the proposed LCC-S compensated IPT system can achieve high efficiency against the fluctuation of transmitter coil inductance. In traditional switch-controlled capacitor, high- frequency current sensor is required for the synchroniza- tion between the transmitter coil current and the driver signals of the switch-controlled capacitor. Nevertheless, the drive signals of D-SCC can be generated directly by the DSP controller in the primary side without detecting zero-cross points of the transmitter coil current, which can improve the system reliability and reduce the cost. Furthermore, the MEPT based on D-SCC is easy to be implemented because only the input dc current measure- ment is required. A 3.3-kW prototype is presented to verify the validity of the proposed D-SCC based MEPT.

Grid-connected inverters are the key part in renewable energy power generation systems. Usually, phase-locked loop (PLL) is adopted in grid-connected inverters to achieve synchronization. However, prior-art works have revealed that the negative resistance behavior in the low-frequency band caused by PLLs may lead to system instability under weak grids. In this article, first, a comprehensive small-signal output impedance modeling of the LCL -filtered single-phase grid-connected inverter is derived for stability analysis, where the digital control delays and PLL dynamics have been taken into account. Then, a simple but effective virtual series-based impedance reshaping method is proposed. With that, the inverter system can operate stably even under a very weak grid (e.g., short-circuit ratio is as low as 1.2). Compared with the traditional grid impedance compensation by virtually increasing grid resistance or reducing the grid inductance, the proposed method does not require grid impedance estimation and is robust against system parameter variations. Thus, its feasibility is improved. Finally, the experimental tests are carried out on a single-phase 5-kW prototype, validating the effectiveness of the proposed scheme.

The bipolar dc microgrid system is considered a greatly promising solution to interface various renewable energy sources and emerging loads due to its advantages in efficiency and reliability. However, pole voltage imbalance and lack of superior bipolar power conversion topologies limit the development and application of bipolar dc microgrid systems. In this context, this article proposes a family of multiport converters based on voltage-multiplying rectifiers to achieve symmetrical bipolar output voltage and power conversion between renewable energy sources and bipolar buses. In the proposed topologies, single-stage power conversion, without voltage balance feedback control, and a low number of components are obtained. Furthermore, the bulky balancing inductor is eliminated to improve conversion efficiency and reduce the volume of the system. Moreover, the higher voltage gain, smaller input current ripple, and lower voltage stress of semiconductor devices make it ideal for interfacing renewable energy sources with bipolar dc microgrids. The derivation method for the proposed topology family is first introduced. Then, a typical topology in the proposed converter family is analyzed in detail as an example, including the operation principle, steady-state performance, parasitic parameter effects, design considerations, efficiency analysis, control method, loop designing, etc. Finally, a 1-kW prototype is developed and tested to verify the performance of the proposed converter.